Re: [time-nuts] 60Hz mains clocking in computers
Since many of us are not so old as I am, and aren't familiar with the PDP-11 family, I should have mentioned that this happened in the middle 80's. Uno Staver wrote: We bought a bunch of PDP-11/23s as part of a communications network system. After successful acceptance tests in Boston, MA, the systems were commissioned in Sweden with 50Hz AC. To make the RSX-11M O/S time-of-day clock run OK, the developers modified some piece of code. Uno Staver Bill Hawkins wrote: Yes, the whole PDP-11 line used line frequency to update the real-time clock. DEC had a real-time operating system, very useful for emulation of analog process control functions. Of course, an RTOS is more than just the clock. We lost that anchor to real time in the interval between the PDP-11 and NTP or SNTP when the microprocessors took over. All crystal clocks; time of day (social time) set by anybody with a wristwatch. Bill Hawkins -Original Message- From: paul swed Sent: Saturday, December 12, 2009 10:09 PM Talk about dusting off the old brain cells. I seem to remember that the PDP 11/23s did indeed allow the use of the 60 hz as an interrupt for precision timing if that can actually be said. The data general nova 1200 also. Boy thats exposing ones age. On Sat, Dec 12, 2009 at 8:29 PM, Colby Gutierrez-Kraybill co...@astro.berkeley.edu wrote: I'm trying to get to the bottom of whether or not any computing equipment made around the advent of UNIX systems (or any time-slicing system) used the mains cycles of 60Hz as phase lock for the internal system clock. My guess is that perhaps they did not as the computing logic is DC based, but, I have memories of using an 68000 based UNIX system that I thought had its internal clock based off of the 60Hz mains... Not sure the vendor anymore. Thanks, Colby ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] 60Hz mains clocking in computers
Hi My second home computer was a PDP=11/20. The first was a PDP-8E. Both are long gone... Bob -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Uno Staver Sent: Tuesday, April 20, 2010 8:28 AM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] 60Hz mains clocking in computers Since many of us are not so old as I am, and aren't familiar with the PDP-11 family, I should have mentioned that this happened in the middle 80's. Uno Staver wrote: We bought a bunch of PDP-11/23s as part of a communications network system. After successful acceptance tests in Boston, MA, the systems were commissioned in Sweden with 50Hz AC. To make the RSX-11M O/S time-of-day clock run OK, the developers modified some piece of code. Uno Staver Bill Hawkins wrote: Yes, the whole PDP-11 line used line frequency to update the real-time clock. DEC had a real-time operating system, very useful for emulation of analog process control functions. Of course, an RTOS is more than just the clock. We lost that anchor to real time in the interval between the PDP-11 and NTP or SNTP when the microprocessors took over. All crystal clocks; time of day (social time) set by anybody with a wristwatch. Bill Hawkins -Original Message- From: paul swed Sent: Saturday, December 12, 2009 10:09 PM Talk about dusting off the old brain cells. I seem to remember that the PDP 11/23s did indeed allow the use of the 60 hz as an interrupt for precision timing if that can actually be said. The data general nova 1200 also. Boy thats exposing ones age. On Sat, Dec 12, 2009 at 8:29 PM, Colby Gutierrez-Kraybill co...@astro.berkeley.edu wrote: I'm trying to get to the bottom of whether or not any computing equipment made around the advent of UNIX systems (or any time-slicing system) used the mains cycles of 60Hz as phase lock for the internal system clock. My guess is that perhaps they did not as the computing logic is DC based, but, I have memories of using an 68000 based UNIX system that I thought had its internal clock based off of the 60Hz mains... Not sure the vendor anymore. Thanks, Colby ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] 60Hz mains clocking in computers
We bought a bunch of PDP-11/23s as part of a communications network system. After successful acceptance tests in Boston, MA, the systems were commissioned in Sweden with 50Hz AC. To make the RSX-11M O/S time-of-day clock run OK, the developers modified some piece of code. Uno Staver Bill Hawkins wrote: Yes, the whole PDP-11 line used line frequency to update the real-time clock. DEC had a real-time operating system, very useful for emulation of analog process control functions. Of course, an RTOS is more than just the clock. We lost that anchor to real time in the interval between the PDP-11 and NTP or SNTP when the microprocessors took over. All crystal clocks; time of day (social time) set by anybody with a wristwatch. Bill Hawkins -Original Message- From: paul swed Sent: Saturday, December 12, 2009 10:09 PM Talk about dusting off the old brain cells. I seem to remember that the PDP 11/23s did indeed allow the use of the 60 hz as an interrupt for precision timing if that can actually be said. The data general nova 1200 also. Boy thats exposing ones age. On Sat, Dec 12, 2009 at 8:29 PM, Colby Gutierrez-Kraybill co...@astro.berkeley.edu wrote: I'm trying to get to the bottom of whether or not any computing equipment made around the advent of UNIX systems (or any time-slicing system) used the mains cycles of 60Hz as phase lock for the internal system clock. My guess is that perhaps they did not as the computing logic is DC based, but, I have memories of using an 68000 based UNIX system that I thought had its internal clock based off of the 60Hz mains... Not sure the vendor anymore. Thanks, Colby ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] 60Hz mains clocking in computers
In 1984 we had a QBUS-based 68000 (dual 68K, due to the paging flaw) that ran 9-track tapes off the end and gained about a good fraction of an hour a day on its clock. We complained to the vendor and they swapped CPU boards for us. Tapes worked fine, and the clock was more accurate, but programs ran slower. Hmmm. Leigh. At 1:44 AM + 12/13/09, time-nuts-requ...@febo.com wrote: Date: Sat, 12 Dec 2009 17:29:17 -0800 From: Colby Gutierrez-Kraybill co...@astro.berkeley.edu Subject: [time-nuts] 60Hz mains clocking in computers To: time-nuts@febo.com Message-ID: 3058527a-cc99-4174-be75-21dd92334...@astro.berkeley.edu Content-Type: text/plain; charset=US-ASCII; format=flowed; delsp=yes I'm trying to get to the bottom of whether or not any computing equipment made around the advent of UNIX systems (or any time-slicing system) used the mains cycles of 60Hz as phase lock for the internal system clock. My guess is that perhaps they did not as the computing logic is DC based, but, I have memories of using an 68000 based UNIX system that I thought had its internal clock based off of the 60Hz mains... Not sure the vendor anymore. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] 60Hz mains clocking in computers
On Sun, Dec 13, 2009 at 07:39:05AM +, Poul-Henning Kamp wrote: In message 2157.12.6.201.67.1260689371.squir...@popaccts.quik.com, J. Forste r writes: I'm not so sure about the Nova 1200. I think all the Novas had the RTC was on a standard I/O board, [...] No, it was an option, but almost everybody bought it, because it was necessary to run any kind of timesharing kernel (RTOS, DOMUS, etc) Technically one could order basic IO boards without some of the functionality - they simply didn't stuff in some of the chips (and more than one customer just added the requisite chips themselves). I do remember that there were some functions on that card that were rarely stuffed... I seem to remember that RDOS (the NOVA disk operating system) DID require the RTC and I certainly don't remember any hacks in the system code to get around the need for timer interrupts to keep time and handle delays and timed waits. It was a real time multitasking kernel, though only one process (mostly) due to the lack of memory management Long time ago though... -- Dave Emery N1PRE/AE, d...@dieconsulting.com DIE Consulting, Weston, Mass 02493 An empty zombie mind with a forlorn barely readable weatherbeaten 'For Rent' sign still vainly flapping outside on the weed encrusted pole - in celebration of what could have been, but wasn't and is not to be now either. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] 60Hz mains clocking in computers
At 1:44 AM + 12/13/09, time-nuts-requ...@febo.com wrote: Date: Sat, 12 Dec 2009 17:29:17 -0800 From: Colby Gutierrez-Kraybill co...@astro.berkeley.edu Subject: [time-nuts] 60Hz mains clocking in computers To: time-nuts@febo.com Message-ID: 3058527a-cc99-4174-be75-21dd92334...@astro.berkeley.edu Content-Type: text/plain; charset=US-ASCII; format=flowed; delsp=yes I'm trying to get to the bottom of whether or not any computing equipment made around the advent of UNIX systems (or any time-slicing system) used the mains cycles of 60Hz as phase lock for the internal system clock. My guess is that perhaps they did not as the computing logic is DC based, but, I have memories of using an 68000 based UNIX system that I thought had its internal clock based off of the 60Hz mains... Not sure the vendor anymore. In the 1980s and 1990s, before networks capable of carrying NTP time to the millions became common, the computer local clock was very often derived from the local AC power mains, and the frequency was steered to match atomic time once per day. The POSIX standards reflect this common approach by the tolerance on CLOCK_REALTIME, 20 milliseconds, this being one cycle of 50 Hz power. The CPU logic clock was not generally phase-locked to the AC power lines, instead being generated by a cheap crystal having a very large tempco. The exception to this was that video generators were (and still are) often locked to the AC line so that hum bars would not drift across the screen. Joe Gwinn ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] 60Hz mains clocking in computers
Joe Gwinn wrote: At 1:44 AM + 12/13/09, time-nuts-requ...@febo.com wrote: Date: Sat, 12 Dec 2009 17:29:17 -0800 From: Colby Gutierrez-Kraybill co...@astro.berkeley.edu Subject: [time-nuts] 60Hz mains clocking in computers To: time-nuts@febo.com Message-ID: 3058527a-cc99-4174-be75-21dd92334...@astro.berkeley.edu Content-Type: text/plain; charset=US-ASCII; format=flowed; delsp=yes I'm trying to get to the bottom of whether or not any computing equipment made around the advent of UNIX systems (or any time-slicing system) used the mains cycles of 60Hz as phase lock for the internal system clock. My guess is that perhaps they did not as the computing logic is DC based, but, I have memories of using an 68000 based UNIX system that I thought had its internal clock based off of the 60Hz mains... Not sure the vendor anymore. In the 1980s and 1990s, before networks capable of carrying NTP time to the millions became common, the computer local clock was very often derived from the local AC power mains, and the frequency was steered to match atomic time once per day. The POSIX standards reflect this common approach by the tolerance on CLOCK_REALTIME, 20 milliseconds, this being one cycle of 50 Hz power. Which does not perfectly match the 60 Hz being used in some countries or for that matter traditional division for PC clocks (derived from 14,31818 MHz, over 4,77 MHz and what the 8253 divider allows). The CPU logic clock was not generally phase-locked to the AC power lines, instead being generated by a cheap crystal having a very large tempco. The exception to this was that video generators were (and still are) often locked to the AC line so that hum bars would not drift across the screen. I have never seen this in any of the devices I've seen. It is certainly not what we do in the TV world either. Examples would be good. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] 60Hz mains clocking in computers
In message 4b251964.5040...@rubidium.dyndns.org, Magnus Danielson writes: Joe Gwinn wrote: The exception to this was that video generators were (and still are) often locked to the AC line so that hum bars would not drift across the screen. I have never seen this in any of the devices I've seen. It is certainly not what we do in the TV world either. Examples would be good. This feature disappeared with color television, specifically NTSC, which tweaked the vertical frequency just a tad lower than 60Hz. Poul-Henning PS: But NTSC gave us the 14.31818181.. MHz frequency, as imortalized by the ghastly colors of the IBM CGA. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 p...@freebsd.org | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] 60Hz mains clocking in computers
Poul-Henning Kamp wrote: In message 4b251964.5040...@rubidium.dyndns.org, Magnus Danielson writes: Joe Gwinn wrote: The exception to this was that video generators were (and still are) often locked to the AC line so that hum bars would not drift across the screen. I have never seen this in any of the devices I've seen. It is certainly not what we do in the TV world either. Examples would be good. This feature disappeared with color television, specifically NTSC, which tweaked the vertical frequency just a tad lower than 60Hz. That ghastly horrible 1000/1001 factor which plauge us still today. The PAL hack to the same problem has less withstanding effects. Whenever they did the HDTV standard they failed to keep the number magic of digital SDTV (i.e. 13,5 MHz and 18 MHz in BT.601). While that solution solve the technical problem, they solved in a bad way and we still stuffer even when the original reason for the solution have disappeared. Poul-Henning PS: But NTSC gave us the 14.31818181.. MHz frequency, as imortalized by the ghastly colors of the IBM CGA. Most people saw CGA using RGBI monitors, so I think it is a bit unfair connection. Regardless, it was never the interface of precission colours. Things got better when IBM used the INMOS G171 for the VGA LUT and DAC. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] 60Hz mains clocking in computers
Industrial process control requires that event time stamps be close to the correct social (wall clock) time, for correlation with events that were not digitized. Computers at the heart of these control systems were required to run on DC from batteries, and so the real-time clock was derived from a local crystal. (Make that micro-computers. Work was still done with line-frequency-aware computers.) The system that I helped design had a clock rate adjustment for social time, expressed as one byte. The user was able to adjust the clock rate for the desired accuracy. A clever algorithm minimized the amount of code added to the clock interrupt routine. But, I have only studied one of the elephant's legs. Bill Hawkins ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] 60Hz mains clocking in computers
On 12/13/09 7:52 AM, Joe Gwinn joegw...@comcast.net wrote: At 1:44 AM + 12/13/09, time-nuts-requ...@febo.com wrote: Date: Sat, 12 Dec 2009 17:29:17 -0800 From: Colby Gutierrez-Kraybill co...@astro.berkeley.edu Subject: [time-nuts] 60Hz mains clocking in computers To: time-nuts@febo.com Message-ID: 3058527a-cc99-4174-be75-21dd92334...@astro.berkeley.edu Content-Type: text/plain; charset=US-ASCII; format=flowed; delsp=yes The CPU logic clock was not generally phase-locked to the AC power lines, instead being generated by a cheap crystal having a very large tempco. The exception to this was that video generators were (and still are) often locked to the AC line so that hum bars would not drift across the screen. Only for black and white TV before color. The frame rate of pre color TV was chosen to be 60 Hz so that hum bars wouldn't move. BUT, come color in the early 50s, and the move to 59.94 Hz (which was as close as you could get with integer division ratios from the master reference, which had something to do with solving a problem with color encoding), there's a slight difference. So that line frequency interference slowly crawls up the screen in 20 seconds. Now, most people who are not time-nuts would say that 59.94 and 60 are the same, but to us, that's a 1000 ppm difference. Woe to the person these days who tries to sync line frequency widgets (like synchronous motors) to video and film cameras (film is nominally 24fps, but if they're shooting for conversion to video, they'll sync to .999*24fps, so that the 3:2 pulldown matches the video, without having to do the dropframe thing to keep it lined up.).. I haven't done much of this in the last 15 years, but in the early 90s, there were directors of photography who used quartz locked cameras and those who didn't. Shooting with video monitors in the scene was always tricky to make sure that the vertical retrace was synced with the camera shutter; which you'd usually do by just starting the camera several times until you got the right phase or changing the camera speed slightly (by eye.. On a film camera, the viewfinder shows you the scene when the film isn't exposing. So your eye is the detector of the optical sampler.) The fancy lock boxes had a phasing knob. I got my start in the special effects business doing graphics software on modified DOS boxes that I could phase lock to the camera sync. Somewhere out in the garage I have a bunch of CGA and VGA cards with external oscillator inputs. The other strategy was to run the monitors at 24fps, and genlock the video to the camera sync output (but that was expensive, you'd only see that in feature films or long duration series..). There were some VGA cards that you could reprogram the sync rates to 24fps, too, but you had to make sure the monitor could actually lock it (and usually, you'd run a little program that started at 30fps and slowly moved it to 24, so the monitor wouldn't assume it had lost lock and try to resync) As chroma-key became cheaper and easier, a lot of times, they'd just paint the screen of the monitor blue or green, and do it in post. I'm out of that business now, but I'll bet that doing it in post is by far the most common these days. It's easy to do the projective geometry needed to warp the desired image to whatever it is in the scene (you click on the 4 corners in a key image, and the software tracks it as it moves, so you don't have to worry about camera moves) ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] 60Hz mains clocking in computers
Dear Jim, Another overlap in our past. Back when I was at UCLA I helped the Ethnomusicology dept with their filming along with synced sound. This was in 1963-64. I designed and built a crystal sync system using the newly available RTL logic ICs. I then modified a 16mm Arri to use it to precisely drive the DC motor because the Arri of course had a 60Hz sync generator built in that would be fed to the Nagra for sound. I phase locked the 60Hz to the divided down discrete 10MHz crystal oscillator I built and thus controlled the speed of the DC motor. It worked very well. The precise 60Hz could be directly sent to the Nagra for the sync track or a separate identical crystal controlled 60Hz source could be right at the Nagra. I took this to the business offices of Eclair in Hollywood and tried to get them to buy or license my idea. They told me that this precision was unnecessary. I was young and not business savy so I did not know to have them sign a non-disclosure. The next year, they came out with exactly what I had showed them. Best Regards, Jeffrey Pawlan ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] 60Hz mains clocking in computers
At 4:53 PM + 12/13/09, time-nuts-requ...@febo.com wrote: Date: Sun, 13 Dec 2009 17:42:12 +0100 From: Magnus Danielson mag...@rubidium.dyndns.org Subject: Re: [time-nuts] 60Hz mains clocking in computers To: Discussion of precise time and frequency measurement time-nuts@febo.com Message-ID: 4b251964.5040...@rubidium.dyndns.org Content-Type: text/plain; charset=ISO-8859-1; format=flowed Joe Gwinn wrote: At 1:44 AM + 12/13/09, time-nuts-requ...@febo.com wrote: Date: Sat, 12 Dec 2009 17:29:17 -0800 From: Colby Gutierrez-Kraybill co...@astro.berkeley.edu Subject: [time-nuts] 60Hz mains clocking in computers To: time-nuts@febo.com Message-ID: 3058527a-cc99-4174-be75-21dd92334...@astro.berkeley.edu Content-Type: text/plain; charset=US-ASCII; format=flowed; delsp=yes I'm trying to get to the bottom of whether or not any computing equipment made around the advent of UNIX systems (or any time-slicing system) used the mains cycles of 60Hz as phase lock for the internal system clock. My guess is that perhaps they did not as the computing logic is DC based, but, I have memories of using an 68000 based UNIX system that I thought had its internal clock based off of the 60Hz mains... Not sure the vendor anymore. In the 1980s and 1990s, before networks capable of carrying NTP time to the millions became common, the computer local clock was very often derived from the local AC power mains, and the frequency was steered to match atomic time once per day. The POSIX standards reflect this common approach by the tolerance on CLOCK_REALTIME, 20 milliseconds, this being one cycle of 50 Hz power. Which does not perfectly match the 60 Hz being used in some countries or for that matter traditional division for PC clocks (derived from 14,31818 MHz, over 4,77 MHz and what the 8253 divider allows). The CPU logic clock was not generally phase-locked to the AC power lines, instead being generated by a cheap crystal having a very large tempco. The exception to this was that video generators were (and still are) often locked to the AC line so that hum bars would not drift across the screen. I have never seen this in any of the devices I've seen. It is certainly not what we do in the TV world either. Examples would be good. It was certainly true in black and white TVs, and I'm pretty sure that the early Macintosh computers did the same. NTSC color TV runs almost at 60 Hz, so the hum bars drift slowly enough to not be visually disturbing. The Television Handbook will have the relevant standards for TV. Because NTSC was intended for North America, behavior with 50 Hz power was not a concern. European standards are different, but they must have dealt with hum bars somehow. When all the vacuum tubes (except the picture tube) disappeared from TVs, hum bars became far less of a problem, and subsequent TV standards don't worry about the effect. Joe Gwinn ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] 60Hz mains clocking in computers
I'm trying to get to the bottom of whether or not any computing equipment made around the advent of UNIX systems (or any time-slicing system) used the mains cycles of 60Hz as phase lock for the internal system clock. My guess is that perhaps they did not as the computing logic is DC based, but, I have memories of using an 68000 based UNIX system that I thought had its internal clock based off of the 60Hz mains... Not sure the vendor anymore. Thanks, Colby ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] 60Hz mains clocking in computers
On 12/12/09 5:29 PM, Colby Gutierrez-Kraybill co...@astro.berkeley.edu wrote: I'm trying to get to the bottom of whether or not any computing equipment made around the advent of UNIX systems (or any time-slicing system) used the mains cycles of 60Hz as phase lock for the internal system clock. My guess is that perhaps they did not as the computing logic is DC based, but, I have memories of using an 68000 based UNIX system that I thought had its internal clock based off of the 60Hz mains... Not sure the vendor anymore. There were a variety of computers synchronized not to the mains frequency but to the horizontal retrace or vertical frame rate for video. That way, they could do things like DRAM refresh or video buffer updates in a clock synchronous way. To a certain extent, even the IBM PC was built like this, running at 4.77 MHz, divided down by 3 from a 14.3 MHz crystal (which was divided by 4 to get the 3.58 MHz color burst). If I had to guess, at the low end, boxes like the Atari 68K machines, at the high end, 3Rivers PERQ (but that one sticks as using 2901 bitslice...) Anything intended to generate video for integration with other video streams would greatly benefit from being able to be synchronized to the NTSC 59.95 Hz frame rate, and if the video memory is the same as the system ram, then running the CPU clock at an exact multiple makes designing the memory access arbiters easier (they can be synchronous), so what you really want is the pixel rate being a multiple of 59.95 and the CPU clock being a multiple of the pixel rate, so that wait state generation is easy (or you can do transparent/hidden access to RAM during a time when you KNOW the CPU won't be looking at it). More than one system used the video access to do DRAM refresh, too. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] 60Hz mains clocking in computers
Not Linux but cpm, I think the poly 88 a 6 slot s-100 computer used the mains for the RTC that is a diode from the secondary of the main power transformer to an interrupt on the processor a 8080. Sure that was used for other computer Real Time Clocks but don't remember any processor clock based on the mains. Stanley - Original Message From: Colby Gutierrez-Kraybill co...@astro.berkeley.edu To: time-nuts@febo.com Sent: Sat, December 12, 2009 7:29:17 PM Subject: [time-nuts] 60Hz mains clocking in computers I'm trying to get to the bottom of whether or not any computing equipment made around the advent of UNIX systems (or any time-slicing system) used the mains cycles of 60Hz as phase lock for the internal system clock. My guess is that perhaps they did not as the computing logic is DC based, but, I have memories of using an 68000 based UNIX system that I thought had its internal clock based off of the 60Hz mains... Not sure the vendor anymore. Thanks, Colby ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] 60Hz mains clocking in computers
co...@astro.berkeley.edu said: I'm trying to get to the bottom of whether or not any computing equipment made around the advent of UNIX systems (or any time-slicing system) used the mains cycles of 60Hz as phase lock for the internal system clock. The IBM 360s bumped a memory location each cycle of the power line. They bumped it by 6 in 50 HZ countries and by 5 in 60 HZ countries. So the units were 300ths of a second. I think that was used for the system time-of-day clock. (I assume it was a few lines of microcode.) My guess is that perhaps they did not as the computing logic is DC based, but, I have memories of using an 68000 based UNIX system that I thought had its internal clock based off of the 60Hz mains... Not sure the vendor anymore. I'm not sure what DC based means. For something like this, you would need an IO device that generated an interrupt. It's a pretty simple IO device, but as far as the CPU is concerned, the power line is part of the outside world. Most of the hardware for this sort of IO device would probably be filtering out noise. -- These are my opinions, not necessarily my employer's. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] 60Hz mains clocking in computers
Talk about dusting of the old brain cells. I seem to remember that the PDP 11/23s did indeed allow the use of the 60 hz as an interrupt for precision timing if that can actually be said. The data general nova 1200 also. Boy thats exposing ones age. On Sat, Dec 12, 2009 at 8:29 PM, Colby Gutierrez-Kraybill co...@astro.berkeley.edu wrote: I'm trying to get to the bottom of whether or not any computing equipment made around the advent of UNIX systems (or any time-slicing system) used the mains cycles of 60Hz as phase lock for the internal system clock. My guess is that perhaps they did not as the computing logic is DC based, but, I have memories of using an 68000 based UNIX system that I thought had its internal clock based off of the 60Hz mains... Not sure the vendor anymore. Thanks, Colby ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] 60Hz mains clocking in computers
Yes, the whole PDP-11 line used line frequency to update the real-time clock. DEC had a real-time operating system, very useful for emulation of analog process control functions. Of course, an RTOS is more than just the clock. We lost that anchor to real time in the interval between the PDP-11 and NTP or SNTP when the microprocessors took over. All crystal clocks; time of day (social time) set by anybody with a wristwatch. Bill Hawkins -Original Message- From: paul swed Sent: Saturday, December 12, 2009 10:09 PM Talk about dusting off the old brain cells. I seem to remember that the PDP 11/23s did indeed allow the use of the 60 hz as an interrupt for precision timing if that can actually be said. The data general nova 1200 also. Boy thats exposing ones age. On Sat, Dec 12, 2009 at 8:29 PM, Colby Gutierrez-Kraybill co...@astro.berkeley.edu wrote: I'm trying to get to the bottom of whether or not any computing equipment made around the advent of UNIX systems (or any time-slicing system) used the mains cycles of 60Hz as phase lock for the internal system clock. My guess is that perhaps they did not as the computing logic is DC based, but, I have memories of using an 68000 based UNIX system that I thought had its internal clock based off of the 60Hz mains... Not sure the vendor anymore. Thanks, Colby ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] 60Hz mains clocking in computers
In message 3058527a-cc99-4174-be75-21dd92334...@astro.berkeley.edu, Colby Gut ierrez-Kraybill writes: I'm trying to get to the bottom of whether or not any computing equipment made around the advent of UNIX systems (or any time-slicing system) used the mains cycles of 60Hz as phase lock for the internal system clock. They sure did. Digitals PDP computers had a counter register which counted mains-cycles as the only sort of real-time-clock. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 p...@freebsd.org | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] 60Hz mains clocking in computers
I'm not so sure about the Nova 1200. I think all the Novas had the RTC was on a standard I/O board, along with the serial interface, PTR, PTP. I remember two crystals, one 16.000 KHz for the clock. The other was for the Baud Rate generator, somewhere about 1 MHz. A minimal system had 3 cards (CPU, Memory, and I/O) -John = Talk about dusting of the old brain cells. I seem to remember that the PDP 11/23s did indeed allow the use of the 60 hz as an interrupt for precision timing if that can actually be said. The data general nova 1200 also. Boy thats exposing ones age. On Sat, Dec 12, 2009 at 8:29 PM, Colby Gutierrez-Kraybill co...@astro.berkeley.edu wrote: I'm trying to get to the bottom of whether or not any computing equipment made around the advent of UNIX systems (or any time-slicing system) used the mains cycles of 60Hz as phase lock for the internal system clock. My guess is that perhaps they did not as the computing logic is DC based, but, I have memories of using an 68000 based UNIX system that I thought had its internal clock based off of the 60Hz mains... Not sure the vendor anymore. Thanks, Colby ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
