PETvet – Operation

To use the PETvet in your PET, you need to remove the 6502 chip from your PET, insert the 6502 into the empty socket on the PETvet (make sure the notch is facing in the same direction as the other chips on the board), and connect the whole PETvet board into the 6502 socket.

The PETvet can be used to halt the CPU of a running PET and view the contents of its memory. This is done by controlling the PETvet microcontroller over a serial port.
The PETvet’s serial port settings are 38400 baud, N81. Connect a serial cable from the PETvet to a computer with a serial port and a terminal program of your choice, using these settings. When you start the PET, you will see a startup message on the terminal which will show you the PETvet switch settings.
At any time while the PET is running, you can halt the CPU and enter diagnostic mode by pressing a key in the terminal. You will then be presented with a menu of options for viewing the contents of the PET’s memory.

Jumper Settings
You can select from the PETvet’s ROM images and memory maps by setting three of the PETvet’s jumpers. The switching jumpers are shown here:
Jumper settings for the PETvet

PETvet default switch settings:

Switch 1 Switch 2 Switch 3 ROM
OFF OFF OFF Basic 2, 40 Column, no CRTC (PET 2001)
OFF OFF ON Basic 4.0, 40 Column, no CRTC (PET 2001)
OFF ON OFF Basic 4.0, 80 Column, CRTC (PET 8032)

Jumper settings and ROM contents can be customized by reprogramming the flash memory on the PETvet’s microcontroller.
To reprogram the PETvet, first remove the PETvet from the PET motherboard.
Move the programming jumper to the left into the “Program” setting as shown:
PETvet Programming Jumper Settings
Connect the PETvet to a terminal, 38400 baud N81. Connect the PETvet to a 5v power source and a message will appear on your terminal indicating that the PETvet is in programming mode.
Start an XMODEM transfer in your terminal program and begin sending the binary that you want to reprogram the PETvet with.
Move the programming jumper back to “Run” mode, and after a second or two you will see the XMODEM transfer begin.
When the transfer is complete, your PETvet is reprogrammed and ready to go.

More details on everything coming soon..

4 Responses to PETvet – Operation

  1. Jac Goudsmit says:

    In case you’re getting the kit version of the PETvet, you can download the assembly manual here.


  2. Mario Keller says:

    How does the board handles bus reactions from the built in components of the PET?
    You need some connection, otherwise the CRT chip could not read the video memory. But how does the board prevent that the internal RAM and the board RAM are not putting data on the same bus lines?


    • bitfixer says:

      Hi Mario,

      The board sets all memory locations which are not specifically replaced by the onboard RAM to passthrough mode. A ’245 buffer switches the CPU connection between the onboard PETvet ram and to the data bus on the mainboard. So anything passed through from the mainboard goes straight to/from the CPU, and the 245 blocks the PETvet ram from talking on the same bus. And vice versa when reading/writing from PETvet ram. Hope this clarifies things.

  3. Bill says:

    I have no signs of life on my CBM 8032. The power supply seems to be working but there is no chirp and the screen is blank. Would the PetVet solve this problem or do I need to at least get life signs before I try it?

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