IO Addresses

The two main sources of information for IO are the two versions of the “The Q1 Assembler” document I am aware of.

Karl’s version (KIO) (only pages 64 to 80), dated 8/78.

From TheByteAttic (TBA): Whole document, marked preliminary, not dated. Pages 47 to 62 describes the IO addresses

The two documents have some differences. For example the known IO addresses are

IO Addresses
Address	KIO	TBA
0x00 (IO)	RTC	Timer
0x01 (IO)	Keyb.	Keyb.
0x03	Disp. data (O)	Disp. data + status (IO)
0x04	Disp. ctrl (IO)	Disp. ctrl (O)
0x05 (IO)	Prt. data + status	Prt. data + status
0x06 (O)	Prt. ctrl 1	Prt. ctrl 1
0x07 (O)	Prt. ctrl 2	Prt. ctrl 2
0x08 (IO)	Dotm. Print
0x09 (IO)	Disk R+W
0x0a (IO)	Disk ctrl 1 + status
0x0b (O)	Disk ctrl 2
0x10 (IO)	serial comms: select control register (O)	Data R+W
0x11 (IO)	serial comms: r/w to comntrol register	ctrl 1, status 1
0x12 (IO)		ctrl 2, status 2
0x13 (O)		ctrl 3
0x19 (IO)		Disk R+W
0x1a (IO)		Disk ctrl 1 + status
0x1b (O)		Disk ctrl 2
0x1c (O)		Disk ctrl 3

Neither seem fully compatible with the JDC roms ROM Images as out commands to both addresses 0xa and 0x1a are in use (see below).

...
0B0B 6C           ; ld l, h         |
0B0C 67           ; ld h, a         |
0B0D D3 1A        ; out (0x1a), a   |
0B0F 97           ; sub a           |
0B10 D3 0A        ; out (0xa), a    |
0B12 DB 1A        ; in a, (0x1a)    |
0B14 0F           ; rrca            |
...

Also I’ve seen in() commands to address 0xc which isn’t documented in either.

Update 2024 10 10

0xc seems to be a printer address - see log entry for 2024 10 10.

Display

When reading the Display status, TBA reports Bit 7 as busy. However KIO has the following:

Bit 6 = 0 for 12 line = 1 for 6 line Bit 5 = 1 for LITE; = 0 for LMC

Neither seem to be complete, as the code for the JDC roms at 0x2A0 seems to be testing Bit 3 to select a 80 character width and Bit 4 to select 40 bytes:

<<<<< Display width? >>>>>
02A0 DB 04        ; in a, (0x4)     |
02A2 CB 5F        ; bit 0x3, a      |
02A4 3E 50        ; ld a, 0x50      |
02A6 C0           ; ret nz          |
02A7 DB 04        ; in a, (0x4)     |
02A9 CB 67        ; bit 0x4, a      |
02AB 3E 28        ; ld a, 0x28      |
02AD C0           ; ret nz          |
02AE C6 07        ; add a, 0x7      |
02B0 C9           ; ret             |

Display status (speculative)
Bit	Description
7	busy
6	1: 6 line, 0: 12 line
5	1: Lite. 0: LMC
4	40 bytes
3	80 bytes
2	unknown
1	unknown
0	unknown