Hello Jim, Not sure about that mask programming option for the chip select pins that "ghaytack" is talking about. If you have a look at the schematic at zimmers.net, you can see that all the 6540 rom have the same chip select configuration: http://www.zimmers.net/anonftp/pub/cbm/schematics/computers/pet/2001/320132-2.gif I have made several - working ;-) - rom adaptors based on the pin configuration of the 6540 rom in that schematic, so I know that it is correct. So if that story about that mask programming option for the chip select pins is true, all the 6540 rom in the PET computers are configured in the same way. These are some of the adaptors I have made: Adaptor for replacing a single 6540 rom: http://members.lycos.nl/ijmtu/hpbimg/6540replacement.jpg Adaptor for replacing all 6540 roms (also 6550 ram adaptor in that picture): http://members.lycos.nl/ijmtu/hpbimg/pet2001rom_ram_Rep.jpg Schematic of 6540 roms replacement: http://img13.imageshack.us/img13/3223/6540romreplacementwith2.gif -donni ----- Original Message ----- From: "Jim Brain" <firstname.lastname@example.org> To: <email@example.com> Sent: Sunday, August 23, 2009 5:14 PM Subject: 6540 Select Signals (Was: Re: 6550 pinout?) > donni wrote: >> That pinout is not entirely correct. >> Pin 2, 3 and 4 are labeled CS3, CS4 and CS5 in that picture. >> That should be: _CS3, _CS4 and _CS5. >> >> -donni >> >> >> ----- Original Message ----- From: "Spiro Trikaliotis" >> <firstname.lastname@example.org> >> To: "CBM Hackers" <email@example.com> >> Sent: Sunday, August 23, 2009 9:19 AM >> Subject: Re: 6550 pinout? >> >> >>> Hello Jim, >>> >>> * On Sun, Aug 23, 2009 at 01:30:45AM -0500 Jim Brain wrote: >>>> Anyone have a link handy for a 6550? I'm not seeing anything. >>> >>> http://www.cbmhardware.de/cbmpet/cbm2001mos.php?Lang=D&from=pet2001 >>> > Spiro, thanks, it appears I found that link via: > > http://forum.6502.org/viewtopic.php?t=212 > > but, the php3 in there caused a redirect. > > Donni, I modeled my 6540 adapter after your via (!CS3,!CS4,!CS5), but > both of our views tend to contradict the poster "ghaytack" in the above > thread. For context: > > "The 6540 were somewhat strange (but useful!) mask programmed ROMS made > by Commodore. They are basically 1Kx8 but have 28 pins! This comes from > the fact that they have several chip select pins. *To make life easier > for system designers the function of the chip select pins could be > chosen as part of the mask programming option* so you could get four > different 6540's where each has a different combination of active high > and active low select pins. > > This made things a doddle for the designers of the PET as they could > miss out a chunck of addresss decoding for the ROMS and connect the > lower 13 address lines (for 8K) directly to the chips with the A12 > through A9 connected directly to the select pins of ALL the chips. One > 6540 could have (say) pin 26 as an active high CS while it's neighbour > could have pin 26 as active low CS. " > > Can anyone shed any light on the discrepency > > Jim > > > Message was sent through the cbm-hackers mailing list -------------------------------------------------------------------------------- No virus found in this incoming message. Checked by AVG - www.avg.com Version: 8.5.409 / Virus Database: 270.13.64/2320 - Release Date: 08/22/09 18:04:00 Message was sent through the cbm-hackers mailing listReceived on 2009-08-23 18:00:04
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