I'm not sure it's an error. These dumps are reversed engineered. Serial mask is probably a better description but I could see the mask being used to filter out the parity bit. When parity is used you are dealing with 7-bit ASCII.
Use for implementing parity may have been the only known application of the field in the ROM. -- John. On Thu, May 7, 2026, 4:53 AM B 9 <[email protected]> wrote: > On Wed, May 6, 2026 at 6:48 AM John R. Hogerhuis <[email protected]> wrote: > >> The Covington map is from the CompuServe SIG archive. I assume he was >> just a guy that disassembled/reverse engineered the ROM. It was a common >> thing for hobbyists to do when they got a new microcomputer. >> > > John, it took me a while to figure it out, but it seems the "Covington > Map" on bitchin100's wiki > <https://bitchin100.com/wiki/index.php?title=Model_100_System_Map_Part_7_(F5F4-FFEC)> > has been altered with incorrect information. FF8D is definitely SERMASK, > the serial mask as Peter described, not the "RS232 parity control byte". > All other copies of Covington's System Map that I could find did not > include that error. > > The Living M100SIG > <https://github.com/LivingM100SIG/Living_M100SIG/blob/main/M100SIG/> has > Robert Covington's M100 RAM map in a file called > Lib-08-TECH-PROGRAMMING/100RAM.RDC > <https://github.com/LivingM100SIG/Living_M100SIG/blob/main/M100SIG/Lib-08-TECH-PROGRAMMING/100RAM.RDC>. > The file's timestamp is 07/31/88 (according to the 100ROM.ARC archive) and > the revision date written at the top of the text is "09/30/85". Club100 > <https://www.club100.org/library/libref.html>'s library reference page > has a copy of the same file, renamed to rcmap7.100 > <https://ftp.whtech.com/club100/ref/rcmap7.100>. (Side note: Although it > has the same date of "09/30/85" written in it, the Club100 version contains > a few typos. The other rcmap files on Club100 have similar minor > deficiencies.) In Club100's "user uploads" there are two references to a > system map, one of them is merely a text file with a dead link > <https://www.club100.org/memfiles/index.php?action=view&filename=Mod100_System_MAP.txt&directory=Don%20Fox> > and the other is a mushed together version > <https://www.club100.org/memfiles/index.php?&direction=0&order=nom&directory=Mike%20Nugent> > of all the Covington map files with very minor changes, mostly reformatting > paragraphs to make it use less paper when printed. (Thank goodness for > wdiff!) > > > On Wed, May 6, 2026, 1:05 AM Peter Noeth <[email protected]> wrote: > >> I have seen the notation in the "Covington ROM Map", and I believe this >> is where Ken got the same notation in his ROM listing (in his personal >> library on the Club100 page). But it doesn't seem that Robert Covington >> ever wrote a book on the Model 100. For such a detailed ROM listing, I >> would have expected that he would have. He must have been involved in >> accessories for the Model 100 in some capacity. >> > > A reasonable question given that the most durable artifacts we have now > are books. I researched it a bit and here's what I found. > > The M100 appears to have had a large and thriving community which shared > their knowledge using the technology of the time: Newsletters, magazines, > BBSes, and CompuServe. Digital documents were newborn then and not all of > them made the transition to our modern Internet. We have no way of knowing > how many "incunabula" may have been lost. Some of the most important > documents are preserved in the Living M100SIG, but unfortunately that > archive is not yet easily usable or discoverable. (Personally, I search the > M100SIG by using `rgrep` on a local git repository.) > > Robert Covington was a technical writer and did publish quite a bit, but > if he wrote a book, I cannot find it. Portable Computing Magazine published > a series of his articles entitled "A Portable Machine" on machine language > programming for the Model 100. We know this to be the case because they are > referred to in the July 1985 issue of PCM which has an index > <https://archive.org/details/PCM-Magazine/1985-07_v3n1/page/58/mode/1up?q=covington> > of the previous two years, however the issues themselves are (for the > moment) lost works: > > Covington, Robert D. “The portable machine - part 1. " (1984, December) p. > 34 —Machine language tutorial. > Covington, Robert D. “The portable machine - part 2. " (1985, January) p. > 38 > Covington, Robert D. “The portable machine - part 3. " (1985, March) p. 25 > Covington, Robert D. "The portable machine - part 4. ” (1985, April) p. 31 > Covington, Robert D. “The portable machine - part 5. ” (1985, June) p. 31 > —Tutorial about the Model 100 display memory map. > > The July 1985 issue also contains an excellent tutorial by Covington > <https://archive.org/details/PortableComputingMagazineJul1985/page/n49/mode/1up> > on how the Model 100 ROM handles keyboard input. In the article he mentions > that the ROM subroutines are listed in his "Great Memory Map", which sounds > to me like the document we now refer to as the "Covington ROM Map". The > "author bio" mentioned that Covington had just finished writing a book on > Model 100 assembly language. I'm guessing that the series he had just > published in PCM were that chapters of his book and his famous Memory Map > was meant to be supplemental material. > > Did his book ever get printed? I don't know. One would think he'd have > advertised it in PCM if he had, but I see nothing like that. It's quite > possible that by 1985 he couldn't find publishers willing to bite on a book > aimed at developers for a rapidly shrinking market. Over a year beforehand, > in May 1984, Portable Computing Magazine had broadened its focus from > solely the Model 100 to include the DOS based Tandy 2000 and Robert > Covington had started publishing a second series in PCM, "Subroutine City", > exploring the intricacies of MS-DOS and the BIOS. A year later, in July of > 1986, PCM's anniversary index of articles for the entire year shows only > one entry under the "Portables" heading: > > Covington, Robert D. “The portable machine - part 6.” (1985, July) p. 50 — > Machine language hints. > > That article had ended with Covington saying, > >> *“So far I have discussed two of the three most used devices in the Model >> 100: the display and the keyboard. Next month, I'll discuss the RS-232/ >> Modem and its ROM routines.”* > > However, the next month, August 1985, only "Subroutine City" for the Tandy > 2000 was published in PCM and Covington's promised Model 100 content never > saw the light of day. That is too bad, particularly because the RS232 ROM > routines have some hairy bits that Covington would have been able to > explain in his clear writing style. > > What happened such that the series got axed abruptly? I cannot find > anything mentioning it. > > I hope someday we do find that he published a book, or at least made it > available somehow, and that it is merely obscure, like the other later > Model 100 writings, such as the books by Tony Anderson > <https://archive.org/details/ProgrammingTipsPeeksAndPokesForTheTandyPortableComputers/mode/2up> > and Mo Budlong > <https://archive.org/details/secrets-of-rom-revealed/page/n5/mode/1up>. > However, both of those authors acknowledge Covington's System Map file but > make no mention of any book. > > Tony B. Anderson described the Covington ROM Map in his 1989 "Programming > Tips > <https://archive.org/details/ProgrammingTipsPeeksAndPokesForTheTandyPortableComputers/>" > book like so, > >> “…the most complete single source was a complete map of the Model 100, >> developed by Robert Covington, and which is available in library 8 of >> CompuServe's Model 100 Forum. The files are named 100ROM.RC0 through >> 100ROM.RC6 (seven files), and 100RAM.RDC, along with the various 100 to 200 >> conversion lists provided by other forum members. Address conversion tables >> have been published in various support magazines; the most complete was in >> the May 1986 issue of Portable 100 magazine.” > > > My guess is that when the book deal fell through, Covington didn't want > all of his hard work to be for nothing and so he released the map to the > community at large. > > —b9 >
