Are there different revisions of RC's map files? I checked [RCMAP7.100] which is the version linked from club100 and didn't see FF8D. I just double checked and I'm still not finding it.
[RCMAP7.100]: https://ftp.whtech.com/club100/ref/rcmap7.100 I also checked the version in the [Living M100SIG] "100RAM.RDC" and it likewise omits FF8D. Do I need to get my eyesight checked? [Living M100SIG]: https://github.com/LivingM100SIG/Living_M100SIG/blob/main/M100SIG/Lib-08-TECH-PROGRAMMING/100RAM.RDC --b9 On May 4, 2026 9:13:02 PM PDT, "John R. Hogerhuis" <[email protected]> wrote: >The Covington ROM map calls it "FF8DH - RS232 parity control byte (1)" > >On Mon, May 4, 2026 at 8:52 PM B9 <[email protected]> wrote: > >> This M100 mouse driver gives an example of knowledge that was once known >> but now seems lost: >> >> https://archive.org/details/P100-Magazine/1990-02/page/10/mode/1up?q=ff8dh >> >> At some point folks knew that FF8Dh was the serial mask. They even had a >> name for it (SERMASK) and a T200 equivalent (FCFCh). >> >> --b9 >> >> >> On May 4, 2026 8:08:14 PM PDT, B9 <[email protected]> wrote: >> >>> Wow, great sleuthing. Which program are you referring to that operates at >>> non-standard rates? >>> >>> In trying to decipher the old listings, I've repeatedly wondered if >>> people had a different ROM disassembly available to them in the past. Of >>> course, it's totally possible that folks were independently figuring things >>> like this out and they simply didn't share the knowledge. >>> >>> By the way, I'm starting a side-project to gather all the known >>> ROM/RAM/IO addresses for the Tandy 200 into a single machine and human >>> readable file. The idea is to have a format that can be used for both >>> disassembling existing code (for example, as "labels" in Ghidra) and as an >>> equiv "library" for writing new assembly language programs. >>> >>> --b9 >>> >>> >>> >>> >>> >>> >>> On May 4, 2026 1:20:19 PM PDT, Peter Noeth <[email protected]> wrote: >>> >>>> Group, >>>> >>>> I have been doing some work on a BASIC program I downloaded from the >>>> old club100 library that uses the RS232 port at a non-standard baud rate. >>>> >>>> The BASIC program also POKES the value 31 into memory location 65421 >>>> (FF8Dh). Since there is no documentation in the code or .DO file, I have >>>> been researching this location. According to Ken Pettit's M100 ROM >>>> disassembly (dated 2013), this memory location is only used twice, once in >>>> the "UART config from text string" routine (17E6h) at 1832h and again at >>>> the "RS232 Receive Interrupt" routine (6DACh) at location 6DB9h. >>>> >>>> The memory location FF8Dh is noted as "RS232 Control Byte" in both >>>> locations in the disassembly, but in reality, is a "read data mask". >>>> Microsoft included this ability, but who knows why. Without the original >>>> commented ROM listing we will never know. >>>> >>>> In the "UART Config From Text String" routine, the value 255 (FFh) is >>>> always written to memory at FF8Dh, which couldn't be a shadow of the RS232 >>>> Control Byte (baud rate, parity, etc.). And in the "RS232 Receive >>>> Interrupt" routine, after data is read from the UART Receive Data Register >>>> (C8h), it is ANDED with the byte at FF8Dh before being stored in the C >>>> Register. Definitely a "mask" operation. >>>> >>>> The BASIC program is putting a value of 31 (00011111b) in FF8Dh, >>>> masking whatever data is received to a value between 0 and 31. This would >>>> make sense to the BASIC program which is configuring the RS232 port for >>>> 5-bit operation. But I would think it is not necessary. Unfortunately, I >>>> can't contact the originator of the BASIC program, to find out why he did >>>> this and how he found this memory location in RAM as I have found no Model >>>> 100 documentation that references it (I own most all of the books written >>>> about the Model 100). >>>> >>>> So, just a "word to the wise" about the function of memory location >>>> 65421 (FF8Dh). Maybe Ken and others who have worked on commenting the >>>> disassembly of the Model 100 ROM, will update their listings. >>>> >>>> Regards, >>>> PeterN >>>> >>>
