That's what the lengthy discussion with Brian is about; if /OE and /PGM disables data out then a 27C64 should work.
Unlikely, but possible; more likely that Georg's board is revised and only uses 2 active-low chip selects. On Mon, Nov 14, 2022 at 11:54 AM Stephen Adolph <twospru...@gmail.com> wrote: > Very interesting Georg, > Can you take some photos of thr PCB sometime if you happen to have your > machine open? > It is a bit of a pain to reassemble I know. > > How did you determine that a 27C64 worked in > M13 socket? Besides the obvious that it does work. > > Because the schematic does not seem to indicate that. Maybe your board is > very different. > > Thx > Steve > > On Monday, November 14, 2022, Georg Käter < > georg.kae...@gk-engineering-services.de> wrote: > >> Hello together, >> >> >> >> my Tandy 200 (European version, build in 1985) uses main PCB >> #-PLX178AHIX. This board accepts >> >> standard UV-eraseable EPROM 27C256 (32kB) and 27C64 (8kB) 150ns type w/o >> any modification. >> >> Maybe there are other revisions of PCB with different EPROM pinout I´m >> not aware of. >> >> >> Regards >> >> Georg >> >> Georg Käter >> Gangolfsweg 44 >> <https://www.google.com/maps/search/Gangolfsweg+44+%0D%0AD-52076+Aachen?entry=gmail&source=g> >> D-52076 Aachen >> Tel. : +49 2408 7194987 >> Fax. : +49 2408 7196758 >> Mobil : +49 171 4839954 >> E-Mail : >> georg.kae...@gk-engineering-services.de >> >> ========== Ihre Nachricht ========================================== >> >> *von* : Brian K. White <b.kenyo...@gmail.com> >> *gesendet* : Montag, 14. November 2022, 16:24 >> *an* : m100@lists.bitchin100.com >> *Betreff* : [M100] custom key mapping generator for Tandy 200 >> >> __________ Originalnachricht _______________________________________ >> >> On 11/14/22 10:11, Brian K. White wrote: >> >> On 11/14/22 09:12, Brian White wrote: >> >> The datasheet says to rest vpp at vcc. Most do, even if elsewhere they >> >> also say that writing is disabled as long as vpp is below vpp and the >> >> only low limit is pretty much the same as for any other pin, like 0.5 >> or >> 0.7 below vcc. >> >> derp I mean the low limit is a little below GND or VSS not VCC. >> >> Although a Microchip 27C64 datasheet I happen to be looking at at the > >> moment does actually say the vpp read voltage is min vcc-0.7, max vcc. >> >> >> More derp, I obviously confused VPP with /WE there. >> But pin 27, being /WE (/PGM), still needs to be held at VCC not GND, >> although theoretically any writes should still fail without VPP, but still, >> you just hold /WE at VCC for reads. >> >> >> >> >> __________ Ende Originalnachricht __________________________________ >> >> >> *Vertraulichkeitsinformation: *Diese Nachricht ist vertraulich. Die >> Informationen dieser Nachricht sind ausschließlich für die persönliche >> und vertrauliche Verwendung durch den/die oben genannten Empfänger >> bestimmt. Wenn Sie kein beabsichtigter >> Empfänger sind, bitte lesen, kopieren und verwenden Sie die Nachricht >> nicht. Machen Sie sie nicht anderen >> zugänglich. Bitte informieren Sie uns umgehend über den Zustellfehler und >> senden Sie die Originalnachricht >> per E-Mail an uns zurück. >> >> >> *Confidentiality Notice: *This message is confidential. The information >> contained in this message is intended only for the personal >> and confidential use of the recipient(s) named above. If you are not the >> intended recipient, please do not >> read, copy, or use it and do not disclose it to others. Please inform us >> immediately of the delivery error >> and return the original message to us via e-mail. >> >
