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When an port is read from (with 'IN') or written to (with 'OUT'), it will activate a number of devices external to the
Z80, depending on the port address. In general, devices respond if certain bits in
the binary representation port number are set and/or reset, rather than to a specific port number; this is known as
'partial decoding'. Whilst this makes the decoding hardware easier to make, it does mean that a considerable amount of
congestion has occured in the space available for new peripherals to respond to if they do not wish to clash with any current devices.
The next complication is to do with the Z80's I/O instructions: it is quicker and easier to select
the low 8 bits of the port number than it is to select the high 8 bits; this means that, when outputting to peripherals for which the upper 8 bits
make no difference, this will often be left unset, and may contain garbage. Thus, the 48K ULA, which
responds to all even port addresses, is often referred to as Port #FE, rather than the full
16-bit port #FFFE.
Listed below are some of the available peripherals (including those like the ULA,
which are in every machine), and the bit fields to which they respond. In the table, '-' means 'don't care', '0' means the
bit must be reset for the peripheral to respond, and '1' means it must be set.
All definitions shown below were provided by Erik Kunze, author of the
XZX-Pro emulator.
- Systems:
- Peripheral: 48K ULA.
Port: ---- ---- ---- ---0 (More information).
- Peripheral: Timex TS2068 ULA.
Port: ---- ---- 1111 1110 (Same as 48K ULA).
- Peripheral: Timex TS2068 Display mode.
Port: ---- ---- 1111 1111
- Peripheral: Timex TS2068 Horizontal Select Register.
Port: ---- ---- 1111 0100
- Audio:
- Memory:
- Peripheral: ZX Spectrum +2a / +3 Memory
Port: 01-- ---- ---- --0- (More information).
- Peripheral: ZX Spectrum 128K / +2 Memory
Port: 0--- ---- ---- --0- (More information).
- Peripheral: +3 Memory.
Port: 0001 ---- ---- --0- (More information).
- Disk Controllers:
- Peripheral: +3 FDC (Data).
Port: 0011 ---- ---- --0- (More information).
- Peripheral: +3 FDC (Status).
Port: 0010 ---- ---- --0- (More information).
- Peripheral: Beta 128.
/* Definitions for Beta 128 */
#define P_TRDOS_CMD 0x1f /* Command */
#define P_TRDOS_STATE 0x1f /* State */
#define P_TRDOS_TRACK 0x3f /* Track */
#define P_TRDOS_SECTOR 0x5f /* Sector */
#define P_TRDOS_DATA 0x7f /* Data */
#define P_TRDOS_SYSTEM 0xff /* System */
- Peripheral: +D.
/* Definitions for +D */
#define P_PLUSD_CMD 0xe3 /* Command */
#define P_PLUSD_STATE 0xe3 /* State */
#define P_PLUSD_PAGE 0xe7 /* Memory paging */
#define P_PLUSD_TRACK 0xeb /* Track */
#define P_PLUSD_SYSTEM 0xef /* System register */
#define P_PLUSD_SECTOR 0xf3 /* Sector */
#define P_PLUSD_PRINTER 0xf7 /* Printer data/ready */
#define P_PLUSD_DATA 0xfb /* Data */
- Peripheral: D80.
/* Definitions for D80 */
#define P_D80_CMD 0x81 /* Command (write) */
#define P_D80_STATE 0x81 /* State (read) */
#define P_D80_TRACK 0x83 /* Track (read/write) */
#define P_D80_SECTOR 0x85 /* Sector (read/write) */
#define P_D80_DATA 0x87 /* Data (read/write) */
#define P_D80_SYSTEM 0x89 /* System register (write)*/
- Peripheral: JLO (Status/Command).
Port: ---- ---- 1000 1111
- Peripheral: JLO (Track).
Port: ---- ---- 1001 1111
- Peripheral: JLO (Sector).
Port: ---- ---- 1010 1111
- Peripheral: JLO (Data).
Port: ---- ---- 1011 1111
- Peripheral: JLO (Select).
Port: ---- ---- 1011 0111
- Interfaces:
- Peripheral: +3 Centronics Interface.
Port: 0000 ---- ---- --0-
- Peripheral: Aerco Centronics Interface.
Port: ---- ---- 0111 1111
- Peripheral: ZX Interface I (RS232/Network).
Port: ---- ---- ---1 0--- (More information).
- Peripheral: ZX Interface I (Control).
Port: ---- ---- ---0 1--- (More information).
- Peripheral: ZX Interface I (Microdrive).
Port: ---- ---- ---0 0--- (More information).
- Peripheral: Kempston Joystick.
Port: ---- ---- 000- ---- (More information).
/* Definitions for Kempston joystick */
#define P_KEMPSTON 0x1f /* Port address */
#define B_KEMPSTON 0x20 /* ---- ---- --0- ---- */
- Peripheral: Sinclair Interface II Joysticks.
/* Definitions for Sinclair Joysticks (Interface II) */
#define P_SINCLAIR1 0xeffe /* Port address */
#define B_SINCLAIR1 0x1000 /* ---0 ---- ---- ---- */
#define P_SINCLAIR2 0xf7fe /* Port address */
#define B_SINCLAIR2 0x0800 /* ---- 0--- ---- ---- */
- Peripheral: Multiface I.
/* Definitions for Multiface I */
#define P_MF1_IN 0x9f /* Port address */
#define P_MF1_OUT 0x1f /* Port address */
- Peripheral: Multiface 128.
/* Definitions for Multiface 128 */
#define P_MF128_IN 0xbf /* Port address */
#define P_MF128_IN_V2 0x9f /* Port address (Disciple)
*/
#define P_MF128_OUT 0x3f /* Port address */
- Peripheral: Multiface 3.
/* Definitions for Multiface 3 */
#define P_MF3_IN 0x3f /* Port address */
#define P_MF3_OUT 0xbf /* Port address */
#define P_MF3_BUTTON 0x3f /* Port address */
#define P_MF3_P7FFD 0x7f3f /* Port address */
#define P_MF3_P1FFD 0x1f3f /* Port address */
- Other:
- Peripheral: ZX Printer.
Port: ---- ---- ---- -0--
- Peripheral: Timex
TS2040 / Alphacom 32 Printers.
Port: ---- ---- 1111 1011
- Peripheral: ZX LPrint III.
* Definitions for ZX LPrint III */
#define P_LPRINT_ON 0xfb /* Page in LPRINT ROM */
#define B_LPRINT_ON 0x84 /* ---- ---- 1--- -0-- */
#define P_LPRINT_OFF 0x7b /* Page out LPRINT ROM */
#define B_LPRINT_OFF 0x84 /* ---- ---- 0--- -0-- */
- Peripheral: Grafpad (British Micro).
/* Definitions for Grafpad (British Micro) */
#define P_GRAFPAD_PEN 0xff3f /* Pen up/down */
#define P_GRAFPAD_X 0xffbf /* Pen position X coordinate
*/
#define P_GRAFPAD_Y 0xff7f /* Pen position Y coordinate
*/
- Peripheral: Kempston Mouse.
/* Definitions for Kempston Mouse */
#define P_KMOUSE_BUTTONS 0xfadf /* Port address */
#define B_KMOUSE_BUTTONS 0x0120 /* ---- ---0 --0- ---- */
#define P_KMOUSE_X 0xfbdf /* Port address */
#define B_KMOUSE_X 0x0520 /* ---- -0-1 --0- ---- */
#define P_KMOUSE_Y 0xffdf /* Port address */
#define B_KMOUSE_Y 0x0520 /* ---- -1-1 --0- ---- */
| special thanks to Jonathan Needle for providing updated ZX Spectrum 128K / +2 Memory entries | |