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Adding roms to the 3 empty spots on the Bally mobo


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Since completing my Bally Arcade restoration (well, it was working for a short time, but I am now trouble-shooting and repairing) I've started thinking about upgrades and modifications. I purchased an Astro Basic cart with the 2000 baud jack off of eBay, cart only, and now have the Basic manual and overlay on the way thanks to Allen. I also purchased the Lil' White Ram upgrade, Ulti-Multi cart and MLM cart from Allen also. But since the Bally went down and I've opened it up for repairs, I've also decided to build my own keyboard interface which I will connect to the keyboard edge connector.


This brings me to the topic title. I did a quick search but didn't find anything in the forum, but maybe my keywords were incorrect. Anyway, I just thought I'd start a new thread and people can either answer my questions or point me to an older thread that has the answers.


So, how easy is it to add more roms to the Bally? Is it just a matter of burning programs/games to the correct eprom and installing them and they will show up on the Bally menu like the built-in rom? Or is there more to it? Maybe a rom has to be selected from the keypad?


Is it possible to have a program spread across two roms with one being high and one low for a 16K program? Or are they 4K roms and for 8K you need two with high and low? I find it hard to believe the built-in programs all fit into a 4K rom though.


Has anyone ever bothered to use the empty rom spaces at all? I haven't seen anything and when reading about other upgrades being done, with motherboard pictures, I've yet to see a mobo with any of the 3 open slots filled with eproms. Has this never been done, and if so why?



Edited by Gunstar
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Keyboard expansion upgrade sounds very beneficial. In the old 1980s newsletters there were a few DIY guides on achieving similar but I recall those involved using a separate terminal/computer and interfacing between the two via some shared cassette-line cable. 


I haven't had much time to delve into Bally myself yet, but one excellent guide about rolling out your own ROMs (including for custom games) is here: https://www.rototron.info/retro-eprom-programming-tutorial/


And you can see that to add your application into the main start menu, it is just a few simple lines of assembly... You can make out which lines are required for that in the snippet below.


                                    ; Thanks for Watching                                 
                                    ; Generated by astroimg
                                    ; https://github.com/hxlnt/astrocade
                                    ; Assemble with Zmac 1.3

            INCLUDE "HVGLIB.H"      ; Include HVGLIB library
            ORG     FIRSTC          ; Initialize at beginning of cartridge ROM area
            DB      $55             ; ... with the code for a normal menued cartridge
            DW      MENUST          ; Initialize menu
            DW      PrgName         ; ... with string at PrgName
            DW      PrgStart        ; ... such that selecting the program enters PrgStart
PrgName:    DB      "THANKS"            ; String to be displayed on menu
            DB      0               ; ... which must be followed by 0
PrgStart:   DI                      ; Disable interrupts
            SYSTEM  INTPC           ; Begin interpreter mode
            DO      SETOUT          ; Set output ports
            DB      100*2           ; ... with VBLANK line set to line 100
            DB      72/4            ; ... with color boundary set to this value/4
            DB      00001000b       ; ... with screen interrupts reenabled 
            DO      COLSET          ; Set color palettes
            DW      Palettes        ; ... with the values at Palettes
            DO      MOVE            ; Display graphic
            DW      NORMEM          ; ... starting at the beginning of screen RAM
            DW      100*BYTEPL      ; ... copy 100 lines
            DW      Graphics        ; ... from data at location Graphics
            DO      ACTINT          ; Activate subtimer interrupts
            EXIT                    ; Exit interpreter mode
Loop:       JP      Loop            ; Play infinite loop
Palettes:   DB      $00,$1C,$D5,$AE ; Left color palette (11b, 10b, 01b, 00b)
            DB      $00,$07,$6C,$AE ; Right color palette (11b, 10b, 01b, 00b)
Graphics:                           ; Graphics
            INCLUDE "RETROCA.gfx"


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Thank you very much @MattPilz!


EDIT: The code above will help, but I didn't realize before replying that the link is a tutorial for people that don't already own a proper eprom burner and software. I have all of that and know all of that already, Of course I went back a bit further in time with my eprom burner which connects to my Atari 8-bit computer and software for all of that and the proper eproms already too. I just needed to know how to get them to work if I install them in the empty spots on the Bally. I didn't know if it would be automatic and just appear on the menu or not. On the Atari 8-bit, for example, one can remove the 8K BASIC rom and any other 8K Atari rom can just be dropped in and it will work. I have Star Raiders built into my 1200XL instead of Basic, because I use the far better BASIC XL/XE fro OSS in the cart slot.

Edited by Gunstar
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