CoCo Hardware
References
The Color Computer Reference Manual contains schematics and detailed hardware information. The images below are from the manual.
Hardware Addresses
PIA 0
| FF00 | PIA0_DA | I/O data or direction (depends on control setting) |
| FF01 | PIA0_CA | Control |
| FF02 | PIA0_DB | I/O data or direction (depends on control setting) |
| FF03 | PIA0_CB | Control |
PIA 1
| FF20 | PIA1_DA | I/O data or direction (depends on control setting) |
| FF21 | PIA1_CA | Control |
| FF22 | PIA1_DB | I/O data or direction (depends on control setting) |
| FF23 | PIA1_CB | Control |
SAM
| FFC0:FFC5 | dispMode | Display mode control |
| FFC6:FFD3 | dispOffset | Display offset |
| FFD4:FFD5 | page | Should always be 0 |
| FFD6:FFD9 | cpuRate | Transparent refresh |
| FFDA:FFDD | memSize | Memory size |
| FFDE:FFDF | mapType | Memory map type |
Vectors
These are "ghosted" from the end of the BASIC ROM at BFF0. Since they are unchangeable it is unlikely you will see them referenced in code. Most of the vectors point to RAM, which must be initialized before enabling the interrupt.
The RAM vectors are what programs must change.
Each vector gets 3 bytes in RAM. The first for the "JMP" opcode followed by the address.
| FFFE:FFFF | vectorReset | Reset/Start vector (A827 ROM) |
| FFFC:FFFD | vectorNMI | NMI vector (0109 RAM) |
| FFFA:FFFB | vectorSWI | SWI vector (0106 RAM) |
| FFF8:FFF9 | vectorIRQ | IRQ vector (010C RAM) |
| FFF6:FFF7 | vectorFIRQ | FIRQ vector (010F RAM) |
| FFF4:FFF5 | vectorSWI2 | SWI2 vector (0103 RAM) |
| FFF2:FFF3 | vectorSWI3 | SWI3 vector (0100 RAM) |
| FFF0:FFF1 | vector6809 | 6809 exceptions like divide by 0 (A681 ROM) |
ROM Vectors
The first bytes in ROM hold the addresses for common routines. This allows the routines themselves to move around in ROM from version to version.
The Spectral Associates people, who published the disassemblies of the ROMs, made calls directly into many ROM routines in their games (see Madness and the Minotaur). Their games would have broken if the ROMs had ever changed.
| A000:A001 | POLCAT | Polls the keyboard for a character |
| A002:A003 | CHROUT | Outputs a character to a device |
| A004:A005 | CSRDON | Starts the cassette for reading |
| A006:A007 | BLKIN | Read a block from the cassette |
| A008:A009 | BLKOUT | Write a block to the cassette |
| A00A:A00B | JOYIN | Samples all 4 joysticks |
| A00C:A00D | WRTLDR | Turns on cassette and writes leader |
ROM Routines
| A1C1 | GETKEY | Get key to A. 0 if no key |
| A30A | PRINTCHAR | Print character A to cursor |
| A928 | CLRSCREEN | Clear the screen |