I don’t understand your question re: C64 ROMs. They are all 24 pin, and not a ‘standard’ or ’common’ EPROM pinout although some compatible EPROMs were available at the time. As I mentioned Commodore was producing these chips en masse so they did not care, better to cut the extra 4 unneeded pins and reduce the cost. The C128 used a ‘standard’ or ‘common’ pinout though, the factory would often use EPROMs when they ran out of masked ROMs for these machines.
The PC-1500 ROM is ‘odd’ compared to a plain vanilla ROM as we see most often. As I said these were done to suit the needs of the manufacturer to reduce external decode logic. My point here was that manufactures will made ROMs that were not ‘standard’ or ‘common’. I am aware that masked ROMS are custom parts, that was never in question. My original premise was that IF Kyocera had made the pinout of the optROM socket compatible with a standard EPROM pinout of the era it would have been much easier for 3rd parties to release software that way. It made little sense to make the optROM socket pinout not match a ‘standard’ or ‘common’ EPROM pinout. Judging by the fact Kyocera used standard pinouts on other models like the M10, PC-8201, etc. maybe they saw this was a better route to go? Maybe it was Tandy who insisted on the funky optROM socket to try and have a lock on the software? Jeff Birt From: M100 <[email protected]> On Behalf Of Mike Stein Sent: Wednesday, May 19, 2021 10:32 AM To: [email protected] Subject: Re: [M100] Other things that used the Molex socket Hi Jeff, if the ROMs in a C64 have a 'non-standard' pinout, what is the 'standard' pinout for a 24-pin 64Kb ROM and how are the C64 ROMs and compatible EPROMs different? I think the only 'non-standard' ROM is the character generator but it's used in the 'standard' way AFAIR. It's not really relevant to the 64Kb C64 ROMs but when you talk about a 'standard' are you talking about the pinout or the pin function? By definition mask-programmed ROMs are all custom parts; not only did you specify the data contents but for many ROMs you could also specify the chip select polarities, so it could have a standard pinout but custom select logic. Your PC1500 ROM isn't really that odd; it was not unusual to use multiple selects for partial address decoding and in fact if you look at other Commodore products for example you'll see the same technique used. Even though the pinout may be the same, those ROMs can not be replaced with an EPROM without an adapter. I wonder if the non-standard pinout in the old M100 and the matching option ROM was meant as a form of copy protection; I guess for compatibility they had to keep the option ROM pinout even after switching to the JEDEC standard in the system ROM. On Wed, May 19, 2021 at 9:46 AM Jeffrey Birt <[email protected] <mailto:[email protected]> > wrote: I really doubt MS had anything to do with the ROM pinout. There were several different ROM pinouts back in the day, every manufacture had their own take on it to suit their own needs. For example, all the ROMs in a C64 have a nonstandard pinout. You could get EPROMs to match back in the day, but they were far less common. But Commodore was mass producing them in house so they did not care. I am looking at a Sharp LH5367 ROM at this very moment from the PC-1500. It is very odd, it has a whole raft of chip selects/chip enables some of which are active high, some are active low. This was done to suit the application they were used in to reduce external decoding logic. The ROM inside the original M100 is just a Sharp made, Sharp pinout part. There was no need for them to make the option ROM socket an odd pinout just because they used this Sharp ROM inside. As I mentioned I think Kyocera figured this out fast and went to standard sockets and pinout in later models when they saw the uses the machines were put to. Nothing to do with Microsoft. Jeff Birt From: M100 <[email protected] <mailto:[email protected]> > On Behalf Of Stephen Adolph Sent: Wednesday, May 19, 2021 7:45 AM To: [email protected] <mailto:[email protected]> Subject: Re: [M100] Other things that used the Molex socket Tandy did release software using the strange socket. Multi-solutions for one, multiplan for another. The M100 main ROM also used the strange pinout. Didn't Microsoft supply the programmed M100 Main ROM PROMs to Tandy? I think I read this somewhere, and in fact they released the PROMs with "Microsoft" all over the interface, against Tandy wishes. Tandy was forced to release as is. If this is true then I suspect Tandy had to implement the interface as per the agreement with Microsoft (which would have included pinout). In later versions, they clearly got away from Microsoft 'shackles'. In the end, I don't think Tandy 'chose' the pinout. I think it was pushed on them by Bill. On Wed, May 19, 2021 at 8:34 AM Jeffrey Birt <[email protected] <mailto:[email protected]> > wrote: You are absolutely correct about the cost of a masked ROM w.r.t. an EPROM or PROM. The option ROM socket was not intended for the main system firmware, it was for adding new functionality. Many times this added functionality was in the form of general productivity applications or sometimes it was specific to a particular company for insurance agents, or controlling laboratory equipment. These aftermarket applications would never be released in sufficient quantity to justify a masked ROM and I’m not aware that Tandy ever released any software itself that way. However, both EPROMS and PROMs have been available since the mid-1970s and would have been the choice for these smaller scale software distributions so making the pin out match an industry standard 27C256 would have made more sense, IMHO. I think Kyocera figured this out fast though as all the subsequent machines ditched the funky option ROM socket and used a standard DIP socket with a standard pinout. Jeff Birt From: M100 <[email protected] <mailto:[email protected]> > On Behalf Of Peter Noeth Sent: Tuesday, May 18, 2021 7:30 PM To: Model 100 Discussion <[email protected] <mailto:[email protected]> > Subject: Re: [M100] Other things that used the Molex socket Jeff, You have to remember that the socket was designed for a "Masked ROM", like the Main ROM, which **was** the standard pinout. At that time there were no programable ROMs (PROMs or EPROMs) that had compatible pinouts, due to the circuit changes necessary for the programming function (capacitor "cells" in EPROMS and "fuses" in PROMS) that caused the pinout to change because of internal layout. Computer manufacturers used Masked ROMs to reduce the per chip cost in large quantities, where they didn't expect frequent changes in content. Also I don't remember a 32K EPROM being available in 1983. Most were 8K or less. The initial high cost of producing the "mask" and required minimum quantity order explains why there were not more "option ROMs" from other software houses. The One Time Programable (OTP) PROMs would have been a good choice, but didn't exist in the 32K size, and the OTP EPROMS didn't exist until decades later. I remember this was always a pain in modifying computer "operating systems" in the early days of "turn key" computers. Not a problem with the S-100 Bus systems, as the CPU board was loaded with easy to change EPROM sockets. Regards, Peter ------------------------------ Message: 2 Date: Tue, 18 May 2021 07:36:25 -0500 From: "Jeffrey Birt" <[email protected] <mailto:[email protected]> > To: <[email protected] <mailto:[email protected]> > Subject: Re: [M100] Other things that used the Molex socket. Message-ID: <[email protected] <http://soigeneris.com> > Content-Type: text/plain; charset="UTF-8" Interesting. I think if Kyocera/RadioShack had not chosen to go with the stupid non-standard pinout it would have been a more popular way of distributing custom applications for the machine. The socket itself was a good idea to make putting a chip in more idiot proof. Jeff Birt
