Atari 7800/2600 Monitor Cartridge Homebrew Overview

7800/2600 Monitor Cartridge
By Harry Dodgson

This video by “BallyAlley” is an overview of the “7800/2600 Machine Language Monitor Cartridge” (Version 2) for the Atari 7800 game console. Version 1, of the Monitor was published by Harry Dodgson in 1993. Version 2 was published by Video 61 in 2000.

This video shows how to use this Atari 7800 6502 machine language monitor program to communicate with the 6502. Like the monitor itself, this video is aimed at someone who knows a little about 6502 of programming. However, even someone without such knowledge should be able to gain some insight into the inner workings of this humble and early homebrew Atari 7800 utility program that was released on cartridge when the Atari console homebrew scene was in its earliest infancy.

The three demonstration programs included on the cartridge (Bumper Tanks, Hex Demo and Color Display) are run and the hexadecimal program listings are shown in the monitor. Also, a few of the example programs are typed into the monitor and run. Finally, a few of the monitor’s built-in subroutines are used to show how to generally program the 2600 and 7800 using this cartridge.

I’m sorry about the fuzziness of the close-up video of the TV screen in the later part of the video; it was the best that I could do with my camera. I may remake and expand the later part of the video that is fuzzy by using an Atari 7800 with a direct video capture connection. This would dramatically clear up the video. For now, this is the best that I can do under the circumstances.

The following information is from the over 200-pages of documentation for the Monitor cartridge.

“7800/2600 Monitor Cartridge” Overview

The 7800 Monitor cartridge contains a 32K byte EPROM, an 8K byte RAM chip, a lithium battery for the RAM, and a few miscellaneous parts to make them all work together. The EPROM is logically divided into two sections; one half for 2600 VCS mode and the other half for 7800 Pro System mode. The battery provides power to the RAM chip allowing the programs and data on it to be retained when the power to the 7800 is turned off. The battery is not user-replaceable. The EPROM on the cartridge is socketed however and can be exchanged with updated software without having to replace the entire cartridge.

The 16K of EPROM allocated for 7800 mode contains:

– Version 2.0 of the 7800 Monitor (includes 8 new commands).
– Three graphic demonstration programs.
– Five example programs to help learn the monitor commands.

There is some unused space on the 7800 half of the EPROM which is reserved for future upgrades of the monitor. The 7800 Monitor allows you to enter programs for either 7800 mode or 2600 mode. You can also run and debug programs for 7800 mode easily. To run programs for 2600 mode, you must change to the 2600 mode of the cartridge.

1 Comment

  1. fuegoave on December 13, 2020 at 10:40 pm

    Great interesting video Adam. When we get together we can talk about it.
    I took a look at all your other youtube videos. I didn’t realize you liked old graphics art programs. I wrote some of those back in 80’s with my Atari 400 and 800. Those are what I had thought that I lost and with your donation to me of 410 recorders, i got a 410 working and recovered my files from cassettes. I’ll give you a disk and show you what i had written back then and also some that my daughter and I have just written a few months ago while teaching her some Atari BASIC programming.
    Rick H

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