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System ROM
The first 8K of the Astrocade's memory map ($0000-$1FFF) is dedicated to system ROM, which contains the operating system and the four built-in programs: Scribbling, Calculator, Checkmate, and Gunfight.
The end of the Nutting Manual contains the complete 8K ROM Source Listing. Its table of contents reads as follows:
| Name | Pages | ROM Memory |
|---|---|---|
| Home Video Game Equates | 2–15 | |
| System Routines | 16–94 | $0000 |
| Scribbling | 1–17 | $0E19 |
| Calculator | 1–20 | $1020 |
| Checkmate | 1–30 | $1328 |
| Gunfight | 1–46 |
Better organization and context
System RAM Memory Cells
System RAM memory definitions are located at $4FC8–4FFD in the Nutting Manual source listing (p. 14–15).
| Used by Music Processor | |
|---|---|
| MUZPC | Music Program Counter |
| MUZSP | Music Stack Pointer |
| PVOLAB | Preset Volume for Tones A & B |
| PVOLMC | Preset Volume for Master Oscillator |
| VOICES | Music Voices |
| Counter Timers (used by DECCTS, ACTINT, and CTIMER) | |
|---|---|
| CT0 | Counter Timer 0 |
| CT1 | Counter Timer 1 |
| CT2 | Counter Timer 2 |
| CT3 | Counter Timer 3 |
| CT4 | Counter Timer 4 |
| CT5 | Counter Timer 5 |
| CT6 | Counter Timer 6 |
| CT7 | Counter Timer 7 |
| Used by SENTRY to Track Controls | |
|---|---|
| CNT | Counter Update & Number Tracking |
| SEMI4S | Flag Bits |
| OPOT0 | Pot 0 Tracking |
| OPOT1 | Pot 1 Tracking |
| OPOT2 | Pot 2 Tracking |
| OPOT3 | Pot 3 Tracking |
| KEYSEX | Keyboard Tracking Byte |
| OSW0 | Switch 0 Tracking |
| OSW1 | Switch 1 Tracking |
| OSW2 | Switch 2 Tracking |
| OSW3 | Switch 3 Tracking |
| COLLST | Color List Address for P. B. A |
| Used by STIMER | |
|---|---|
| DURAT | Note Duration |
| TMR60 | Sixtieths of a Second |
| TIMOUT | Blackout Timer |
| GTSECS | Game Time (Seconds) |
| GTMINS | Game Time (Minutes) |
| Used by MENU | |
|---|---|
| RANSHT | Random Number Shift Register |
| NUMPLY | Number of Players |
| ENDSCR | Score to Play to |
| MRLOCK | Magic Register Lockout Flag |
| GAMSTB | Game Status Byte |
| PRIOR | Music Protect Flag |
| SENFLAG | Sentry Control Seizure Flag |
| UMARGT | User Macro Argument Table [??] |
| USERTB | User Table [??] |
System dope vector (valid for ALL system ROM programs)
STIMER EQU $0200 ; Seconds and game TIMER, music CTIMER EQU $0203 ; Custom TIMERs FNTSYS EQU $0206 ; FoNT descriptor for SYStem font FNTSML EQU $020D ; FoNT descriptor for SMaLl font ALKEYS EQU $0214 ; ALl KEYS keypad mask MENUST EQU $0218 ; head of onboard MENU STart MXSCR EQU $021E ; address of 'MaX SCoRe' text string NOPLAY EQU $0228 ; address of 'Number Of PLAYers' string NOGAME EQU $0235 ; address of 'Number Of GAMEs' string
