6502 Assembly programming for the Commodore PET
| The PET was the predecessor to the
VIC 20, Released in 1976 it was the earliest of the Commodore home
computers Later revisions added more memory and a higher screen resolution, though it was still only 'character based' |
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|
 Thanks to "KnightFire66" for the PET photos! |
Memory Map
| From | To | Function |
| $0000 | $3FF | OS and Basic storage |
| $0400 | $1FFF | Basic Program / 8k main ram |
| $2000 | $7FFF | 32k extension |
| $8000 | $83FF | VRAM |
| $C000 | $E7FF | Basic ROM |
| $E800 | $EFFF | I/O |
| $F000
|
$FFFF
|
OS ROM |
Character Map
| Write #12 to $E84C
|
Write #14 to $E84C
|
Keymap
Rom Functions
| Address | Purpose |
| $FFD2 | PrintChar A |
| $FFE4 | ReadChar A |
| $FFCF | Input a character |
I/O Map
| Port | Purpose | Notes |
| $E810
|
Key Row select (0-9) | |
| $E812 | Key Data | |
| $E820 | IEEE488 | |
| $E840 | IO Port B output | |
| $E841 | IO Port A output | |
| $E842 | IO Port B direction (1=out 0=in) | |
| $E843 | IO Port A direction | |
| $E844 | Read Timer 1 Counter L / Write Timer 1 Latch L | |
| $E845 | Read Timer 1 Counter H / Write Timer 1 Latch H | |
| $E846 | Access Timer 1 Counter L | |
| $E847 | Access Timer 1 Counter H | |
| $E848 | Read Timer 2 Counter / Write Timer 2 L byte | 64-255 = Sound Frequency |
| $E849 | Access Timer 2 Counter | |
| $E84A | Serial I/O shift register | 15/51/85 = Sound Octive |
| $E84B | Aux Control Register | 16= Sound On |
| $E84C | Peripheral control | 12=Graphics |
| $E84D | Interrupt Flag Register (IFR) | |
| $E84E | Interrupt enable register | |
| $E84F | IO Port A Output without handshaking | |
| $E880 | CRTC reg select | |
| $E881 | CRTC reg Data | |
| $FFF0 | 64k Expansion Control Register |
Sound
The PET did not have any built in sound, but a speaker can be connected to the IO port.
The PET is capable of up to 4 octaves... one of 3 possible pairs can be selected with $E84A
Address $E84B will turn the sound on or off... we
write #16 to turn it on, #0 to turn it off.
Address $E84A can be used to select the Octave with
value 15/51/85
Address $E848 can be used to select the note, a
value of 64-255 should be passed.
It is not possible to set the volume, or play multiple tones at the same time.
| Note Freq | octave=15 | octave=51 | octave=85 | |||
| Octive 0 | Octive 1 | Octive 1 | Octive 2 | Octive 2 | Octive 3 | |
| B | 251 | 125 | 251 | 125 | 251 | 125 |
| C | 238 | 118 | 238 | 118 | 238 | 118 |
| C# | 224 | 110 | 224 | 110 | 224 | 110 |
| D | 210 | 104 | 210 | 104 | 210 | 104 |
| D# | 199 | 99 | 199 | 99 | 199 | 99 |
| E | 188 | 93 | 188 | 93 | 188 | 93 |
| F | 177 | 88 | 177 | 88 | 177 | 88 |
| F# | 168 | 83 | 168 | 83 | 168 | 83 |
| G | 158 | 78 | 158 | 78 | 158 | 78 |
| G# | 149 | 74 | 149 | 74 | 149 | 74 |
| A | 140 | 69 | 140 | 69 | 140 | 69 |
| A# | 133 | 65 | 133 | 65 | 133 | 65 |
(Sound info taken from the PetFaq)
Sfx with Chibisound!
| These tutorials use a sound 'driver' called ChibiSound, Chibisound uses a single byte parameter in the Accumulator, and provides 64 different pitches, in low or high volume with either tones or noise. Sending a value of 0 mutes sound, all other values make a tone... Chibisound is intended to make it simple to have SFX in multiplatform games and was used in Grime Z80 and Grime 6502 |
|
Writing Chibi Sound!
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on Amazon in Print or Kindle!
Available worldwide!
Search 'ChibiAkumas' on
your local Amazon website!
Click here for more info!
Buy my Assembly programming book
on Amazon in Print or Kindle!
Available worldwide!
Search 'ChibiAkumas' on
your local Amazon website!
Click here for more info!