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Thread: Pet Rescue

  1. #1
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    Default Pet Rescue

    So, friend brought over a PET 2001 ( 6540/2114 v2 ) PCB.. after replaceing all the rusted chips, and corroded rom sockets, I was able to get it backup, of course not only after i toasted my pet vet.

    So, needed to fix my PET since no petvet.. i know I had a bad rom, but didn't remember, so i pulled out the trusty fluke 9010 and did rom tests and found out i had a bad H4, they were also all mixed up, and the part numbers didn't match anything on the net, but the signature(s) match V2 .

    While I wait for the romulator, i picked up some of the 6540 Rom adapter pcb(s) from RETRO Innovations but turns out they don't work out of the box, i had to do some bodge wires to get to work properly, seems the schematic online doesn't match the pcb..


  2. #2
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    Default

    Fluke Signatures: <rom> <sig> <location>

    rom-1-c000.901439-01.bin 1499 LOC H1
    rom-1-c000.901447-01.bin 1499 LOC H1

    rom-2-c000.901439-09.bin B332 LOC H1
    rom-2-c000.901447-09.bin B332 LOC H1

    rom-1-c800.901439-05.bin 6ABE LOC H5
    rom-1-c800.901447-02.bin 6ABE LOC H5

    rom-1-d000.901439-02.bin 3F23 LOC H2
    rom-1-d000.901447-03.bin 3F23 LOC H2

    rom-1-d800.901439-06.bin 6470 LOC H6
    rom-1-d800.901447-04.bin 6470 LOC H6

    rom-1-e000.901439-03.bin 40E0 LOC H3
    rom-1-e000.901447-05.bin 40E0 LOC H3

    rom-1-f000.901439-04.bin 3D98 LOC H4
    rom-1-f000.901447-06.bin 3D98 LOC H4

    rom-1-f800.901439-07.bin 63AC LOC H7
    rom-1-f800.901447-07.bin 63AC LOC H7



    rom-3-c000.901439-13.bin 36D3 LOC H1
    rom-3-c000.901447-20.bin 36D3

    rom-3-c800.901439-14.bin BA97 LOC H5
    rom-3-c800.901447-21.bin BA97

    rom-3-d000.901439-15.bin 4CDB LOC H2
    rom-3-d000.901447-22.bin 4CDB

    rom-3-d800.901439-16.bin 74A5 LOC H6
    rom-3-d800.901447-23.bin 74A5

    rom-3-e000.901439-17.bin BED9 LOC H3
    rom-3-e000.901447-24.bin BED9

    rom-3-f000.901439-18.bin FAFE LOC H4
    rom-3-f000.901447-25.bin FAFE

    rom-3-f800.901439-19.bin B248 LOC H7
    rom-3-f800.901447-26.bin B248

  3. #3
    Join Date
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    Default

    Quote Originally Posted by ki4swy View Post
    ...i had a bad H4, they were also all mixed up, and the part numbers didn't match anything on the net, but the signature(s) match V2 .
    ROM images and part numbers are available in several locations, especially in the 'main' repository of PET stuff:
    http://www.zimmers.net/anonftp/pub/cbm/firmware/computers/pet/index.html

    The 901439-xx ROMs are 6540 versions, numbered by socket number
    The 901447-xx ROMs are the 2316 (2716) versions of the same ROMs, numbered according to address.

    While I wait for the romulator, i picked up some of the 6540 Rom adapter pcb(s) from RETRO Innovations but turns out they don't work out of the box, i had to do some bodge wires to get to work properly, seems the schematic online doesn't match the pcb..


    Interesting; exactly what needed modification? I've used quite a few of his adapters including the 6540/27xx versions and don't recall having to 'bodge' anything.

  4. #4

    Default

    I too would be very interested in the modifications you needed to make to Jim's 6540/27xx adapters as I am in a middle of a project and will be using them.

    With regards to the ROMS, I too found it difficult to figure out which ROM went where because the part numbers and marking didn't fully match with what's on the NET

    My ROMS have MPS 6540 markings then 0xx where xx is a number such as 18,14,12,16,15,13,19 (reading ROMS from left to right)

    This guy posted a photo which helped me confirm things

    http://www.8bit-homecomputermuseum.a...t/bluepet.html
    Last edited by AndyG; May 21st, 2020 at 11:08 PM.

  5. #5
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    Default

    The Adapters came and had the following pin mappings to the LS138:

    6540 Pin , Pin Desc, LS138 Input Pin.
    2 /CS5 -> LS138 PIN 3 C Input
    3 /CS4 -> LS138 PIN 2 B Input
    4 /CS3 -> LS138 PIN 1 A Input
    16 CLK -> LS138 G1 Input
    17 CS2 -> LS138 PIN 4 /G2A Input
    27 CS1 -> LS138 PIN 5 /G2B Input

    LS138 Y3 Output is tied to the EEPROM /OE enable pin, so in order for this pin to be LOW, the Inputs need to be A & B & G1 need to be High, and G2A & G2B need to be low.

    Which if you look at the above pinout, wouldn't happen. The 6540 requires a LOW on 2/3/4 and High on 16/17/27 to for output. in this arrangement, since ABC are low, then Y0 would be low and was hoping i could just ove the LS138 output to Y0 from Y3, but alas, that wouldn't work, becuase /G2 is High, which basically set Y0 to high iqnoring the select inputs.

    So, using the schematic they have posted ( which is valid ) the correct layout would be:

    2 /CS5 -> LS138 PIN 5 /G2B Input ( Active Low for Select )
    3 /CS4 -> LS138 PIN 4 /G2A Input ( Active Low for Select )
    4 /CS3 -> LS138 PIN 3 C Input ( Active Low for Select )
    16 CLK -> LS138 G1 Input ( Active High for Select )
    17 CS2 -> LS138 PIN 1 A Input ( Active High for Select )
    27 CS1 -> LS138 PIN 2 B Input ( Active High for Select )

    This will put the LS138 Y3 LOW for the /OE on the EEPROM.


    I will see if i can make some detailed pictures of the modification, I bought 10 boards hoping to upgrade to Rom 3 .. But having to modify 10 of them seems futile now, i have a 6502 RAM/ROM Boards i ordered from Oshpark that are coming in so can just build my own "petvet" style device.

    these had a (C) of 2012? but doesn't appears ANYBODY ever reported an issue? the silkscreens he has posted are for a Surface mount variant which appear to have the correct traces, just the DIP version is wrong which is the "Blank" pcb option.

  6. #6
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    Dec 2012
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    Brandon, FL
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    Default

    Quote Originally Posted by AndyG View Post
    I too would be very interested in the modifications you needed to make to Jim's 6540/27xx adapters as I am in a middle of a project and will be using them.

    With regards to the ROMS, I too found it difficult to figure out which ROM went where because the part numbers and marking didn't fully match with what's on the NET

    My ROMS have MPS 6540 markings then 0xx where xx is a number such as 18,14,12,16,15,13,19 (reading ROMS from left to right)

    This guy posted a photo which helped me confirm things

    http://www.8bit-homecomputermuseum.a...t/bluepet.html
    Correct, that is the same with mine, thankfully i was able to just use my FLUKE to sign test a rom in each socket and i then labeled what address they belong

    It also helped me identify socket issues in one of the pets.. i ended up replacing all the rom sockets.. it cute when you read an address and the numbers change when you tap on the prom

  7. #7
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    Brandon, FL
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    Another Gotcha, is the PIA for the Keyboard is BACKWARDS from all the other chips... Pin 1 is to the LEFT not the right. Go Figure.

  8. #8
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    Default

    I also ordered a bunch of these:

    http://vic-20.de/x1541/hardware/petram.html

    I will have plenty left over, and can probably pre-program the gals for them.

  9. #9
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    Default

    FYI.. i just got done looking for the PET 2001 scheamtic and added some notes:

    2 /CS5 -> LS138 PIN 5 /G2B Input ( Active Low for Select ) * ALWAYS LOW, could tie to ground.
    3 /CS4 -> LS138 PIN 4 /G2A Input ( Active Low for Select ) * This is tied to SEL /C, /D, /E, /F .. 2001 doesn't have a SEL /B exposed on bus for v4.0 Basic.
    4 /CS3 -> LS138 PIN 3 C Input ( Active Low for Select ) * Used in Conjection with CS1 to select 0x000-0x7ff or 0x800-0xfff if /CS3 is low, then CS1 is tied to Address Buss
    16 CLK -> LS138 G1 Input ( Active High for Select ) * Only needed on 6540 , Used to Latch output, must be AND with address election for a Low on /OE on jedec eeprom
    17 CS2 -> LS138 PIN 1 A Input ( Active High for Select ) * ALWAYS HIGH , could just tie High.
    27 CS1 -> LS138 PIN 2 B Input ( Active High for Select ) * Used in Conjection with /CS3 to select 0x000-0x7ff or 0x800-0xfff if CS1 is high, then /CS3 is tied to Address Buss

  10. #10
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    Boy, I don't know what you've got there but it sure doesn't match my DIP '138 version of the 6540>27xxx adapter; mine are the same as the SMT version except pins 3 and 1 are swapped and pin 9 is the select output instead of pin 12:

    2 > 5
    3 > 4
    4 > 1
    16 > 6
    17 > 3
    27 > 2

    But all you should really need is /CS4 to chip select and /CS3 to A11; you could even replace both halves with a 2732.

    Jim checks in here from time to time; maybe he can shed some light on the discrepancy.

    6540s4.jpg
    Last edited by MikeS; May 22nd, 2020 at 04:21 PM.

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