Spectrum I/O map ================ The Spectrum hardware only partially decodes some of the address lines. The video/sound ULA is selected when A0 is low. The Interface 1 microdrive and serial/network interface is selected with A3 and A4. The Sinclair printer is selected when A2 is low, but an alternative printer interface would use full decoding. The Kempston joystick interface is usually selected by A5. Some interfaces select with A7, A6 and A5, some interfaces fully decode address 31. This shows the full address range available if full address decoding is used working around the partially decoded addresses of other Spectrum hardware, and the addresses of hardware I have built. 76543210 Hex Dec Input Output 11111111 FF 255 User port in User port out 11111110 FE 254 Spectrum keyboard/Tape Border/Sound/Tape 11111101 FD 253 Ascii keyboard data Memory Bank Select 11111011 FB 251 Printer status Printer output 11111001 F9 249 Ascii keyboard status 11110111 F7 247 Int#1 serial/net input Int#1 serial/net output 11101111 EF 239 Microdrive/serial status Microdrive/serial control 11100111 E7 231 Microdrive data Microdrive data 11011111 DF 223 * 11011101 DD 221 * 11011011 DB 219 * 11011001 D9 217 * 10111111 BF 191 10111101 BD 189 10111011 BB 187 10111001 B9 185 10011111 9F 159 * 10011101 9D 157 * 10011011 9B 155 * 10011001 99 153 * 01111111 7F 127 01111101 7D 125 01111011 7B 123 DISCiPLE control DISCiPLE control 01111001 79 121 01011111 5F 95 * 01011101 5D 93 * 01011011 5B 91 * 01011001 59 89 * 00111111 3F 63 00111101 3D 61 00111011 3B 59 00111001 39 57 00011111 1F 31 Kempston Joystick 00011101 1D 29 + 00011011 1B 27 + 00011001 19 25 + * marks addresses that clash with an A5 kempston interface + marks addresses that clash with an A7-A6-A5 kempston interface Port &FF - User Port -------------------- Reading - Input from input lines Writing - Output to output latch Port &FE - Sinclair ULA ----------------------- Reading: The eight high address lines specify which half-row of five keys should be read: Bit 7 6 5 4 3 2 1 0 +---+---+---+-------------------+ | | E | | Key Scan Line | E=Ear +---+---+---+-------------------+ A8 11111110 #FEFE V C X Z SHIFT A9 11111101 #FDFE G F D S A A10 11111011 #FBFE T R E W Q A11 11110111 #F7FE 5 4 3 2 1 A12 11101111 #EFFE 6 7 8 9 0 A13 11011111 #DFFE Y U I O P A14 10111111 #BFFE H J K L ENTER A15 01111111 #7FFE B N M SYM SPACE If a key is pressed, the relevant bit is read as a zero. If the key is not pressed, the bit is read as a one. It is possible to use bits 5 and 7 to access two more columns of keys, giving another 16 keys. Writing: Bit 7 6 5 4 3 2 1 0 +-----------+---+---+-----------+ | | | | B | M | Border | M=Mic, B=Buzzer +-----------+---+---+-----------+ The lowest three bits specify the border colour; a zero in bit 3 activates the MIC output, whilst a one in bit 5 activates the internal speaker. Port &FD - ASCII Keyboard/Memory Select --------------------------------------- Reading: input from ASCII keyboard Writing: Bit 7 6 5 4 3 2 1 0 +---------------+---------------+ | ROM Bank | RAM Bank | External Memory Select +---------------+---------------+ ROM Bank: Memory paged in at &0000 RAM Bank: Memory paged in at &C000 %000n - Internal or External ROM 0-1 %010n - Internal ROM 0-1 %1n0n - External ROM 0-3 OUT &FD,%1xxxxxxx asserts ~ROMCS and prevents other ROMs being accessed. On the Spectrum 128 this results in an internal ROM being selected, but access to it supressed and the specified external ROM is accessed. OUT &FD,%01xxxxxx releases ~ROMCS and allows other ROMs to be accessed. On the Spectrum 128 this results in the internal ROMs being accessed. OUT &FD,%00xxxxxx either asserts or releases ~ROMCS depending on the ROMBox links. If the links are unset internal ROMs are accessed. If the links are set, internal ROMs are overridden and external ROMs are accessed. This allows an external ROM to be present in bank 0 on startup, but still allow access to the internal ROMs in bank 2 and 3. Bit 5 must be zero to prevent the Spectrum 128 paging register being disabled, giving four external ROM banks. If disabling access to the internal ROMs is acceptable, then bit 5 can be used, giving 8 or 16 ROM banks. Note that this means that any access to bank 2 and three will access whichever ROM was last selected before the Spectrum 128 paging register was disabled. With an unmodified Interface 1 or similar hardware, shadow ROMs will only be paged in if ~ROMCS is released by paging in bank 2 or 3 (or 0 or 1 if the ROMBox links are unset). With a modified Interface 1 to provide a secondary ~ROMCS signal, shadow ROMs can be paged in with any bank selected. Bit 7 6 5 4 3 2 1 0 +-------+---+---+---+-----------+ | | D | R | S | RAM Bank | Spectrum 128 Memory Select +-------+---+---+---+-----------+ D: Disable further access R: Memory paged in at &0000 - 0=128k ROM, 1=48k ROM S: Memory displayed as screen - 0=bank 4, 1=bank 7 RAM Bank: Memory paged in at &C000 With the external memory select register sharing the same address as the Spectrum 128 memory select register at &7FFD both can be written to at the same time. If the value written enables an external ROM, then whatever ROM is selected by the Spectrum 128 is overridden. The Spectrum 128 only decodes the top two bits of the address high byte, so a write to %01xxxxxx:&FD writes to the memory select latch. As the Spectrum 128 select latch only responds to the bottom six bits of the data, OUT (&FD),A can be used if A contains a value in the range &40-&7F. A full range of ROM numbers is: %0000 Internal ROM 0/External ROM 0 %1000 External ROM #0 %0001 Internal ROM 1/External ROM 1 %1001 External ROM #1 %0100 Internal ROM 0 %1100 External ROM #2 %0101 Internal ROM 1 %1101 External ROM #3 Port &FB - Centronics Printer ----------------------------- Reading: printer status Bit 7 6 5 4 3 2 1 0 +---+---+---+---+---+---+---+---+ | | | | | | | | | +---+---+---+---+---+---+---+---+ ~BUSY + | | | | ACK -+ | | | ~ERROR --+ | | ~PAPER OUT ---+ +--- SELECTED Writing: data output to printer port, data can be written if IN &FB bit7=1, writing generates STROBE. Port &FB - Sinclair Printer --------------------------- Reading: printer status Bit 7 6 5 4 3 2 1 0 +---+---+---+---+---+---+---+---+ | | | | | | | | | +---+---+---+---+---+---+---+---+ stylus ready --+ | +-- encoder pulse printer not present -+ Writing: printer control Bit 7 6 5 4 3 2 1 0 +---+---+---+---+---+---+---+---+ | | | | | | | | | +---+---+---+---+---+---+---+---+ print a dot --+ | | | +-- slow printer motor +---- stop motor Port &F9 - ASCII Keyboard ------------------------- Reading: keyboard status Bit 7 6 5 4 3 2 1 0 +---+---+---+---+---+---+---+---+ | | | | | | | | | +---+---+---+---+---+---+---+---+ | | | +-- SHIFT | | +---- CONTROL | +------ CAPS +-------- REPEAT Writing: unused Port &F7 - Interface 1 serial input ----------------------------------- Reading: Bit 7 6 5 4 3 2 1 0 +---+-----------------------+---+ |txd| | | | | | |net| +---+-----------------------+---+ txd: input on serial port TXD line net: input on network line Writing: Bit 7 6 5 4 3 2 1 0 +---------------------------+---+ | | | | | | | |out| +---------------------------+---+ out: output to serial port RXD line, or network, or drive select Output selected with &EF bit 0 Port &EF - Interface 1 control ------------------------------ Reading: Bit 7 6 5 4 3 2 1 0 +-----------+---+---+---+---+---+ | | | | | | | | | +-----------+---+---+---+---+---+ | | | | +-- write protect | | | +---- sync | | +------ gap busy --------+ +-------- dtr Writing: Bit 7 6 5 4 3 2 1 0 +-------+---+---+---+---+---+---+ | | | | | | | | | +-------+---+---+---+---+---+---+ | | | | | +-- comms data | | | | +---- comms clock wait ------+ | | +------ r/w cts --------+ +-------- erase Port &E7 - Interface 1 Microdrive data -------------------------------------- Reading: data from microdrive Writing: data to microdrive Port &1F - Kempston Joystick/Input port --------------------------------------- Reading: joystick position Bit 7 6 5 4 3 2 1 0 +---+---+---+---+---+---+---+---+ | | | | | | | | | +---+---+---+---+---+---+---+---+ input bit 7 --+ | | | | | | +-- RIGHT input bit 6 ----+ | | | | +---- LEFT FIRE 2 ------+ | | +------ DOWN FIRE 1 --------+ +-------- UP Writing: unused