Read error b

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{{keywords>amstrad,pcw,hardware,io,address,memory}}
====== I/O Ports ======

|Port (hex)|Direction |Peripheral / Function                                                            |Notes                                                                                          |
|00h       |Read/Write|Floppy Disk Controller (uPD765A) - Main Status Register                          |FDC status register                                                                            |
|01h       |Read/Write|Floppy Disk Controller (uPD765A) - Data Register                                 |FDC data register                                                                              |
|84h       |Read      |Standalone Centronics (CEN) Port - Status                                        |Bit 0: 1=busy / 0=ready                                                                        |
|85h       |Write     |Standalone Centronics (CEN) Port - Strobe                                        |Write byte to 87h then 85h then 87h to toggle STROBE                                           |
|87h       |Write     |Standalone Centronics (CEN) Port - Data                                          |Write data byte here as part of output sequence                                                |
|9Fh       |Read      |Kempston Joystick Interface                                                      |Bit 4=Fire, Bit 3=Down, Bit 2=Up, Bit 1=Left, Bit 0=Right                                      |
|A0h       |Read      |AMX Mouse - Vertical Movement (8255 PPI Port A)                                  |Low nibble=moves up, high nibble=moves down                                                    |
|A0h       |Read      |Multilink Network Interface - Control/Status                                     |Bit 1=byte waiting to send, Bit 0=ready to receive                                             |
|A0h       |Read/Write|Timatic Winchester / SASI (NCR 5380) - SCSI Data                                 |Also used by ASD PCWHD10/20 as Data register (see A0h conflict)                                |
|A0h       |Read/Write|ASD PCWHD10/PCWHD20 - Data Register                                              |Conflicts with Timatic and AMX Mouse                                                           |
|A1h       |Read      |AMX Mouse - Horizontal Movement (8255 PPI Port B)                                |Low nibble=moves right, high nibble=moves left                                                 |
|A1h       |Read/Write|Timatic Winchester / SASI (NCR 5380) - Initiator Command Register                |Also used by ASD PCWHD10/20 as Error/Features                                                  |
|A1h       |Read/Write|ASD PCWHD10/PCWHD20 - Error / Features                                           |Conflicts with Timatic                                                                         |
|A2h       |Read/Write|AMX Mouse - Button State & Reset (8255 PPI Port C)                               |Input: bits 0-2=button states, Output: write FFh then 0 to reset                               |
|A2h       |Read/Write|Timatic Winchester / SASI (NCR 5380) - Mode Register                             |Also used by ASD PCWHD10/20 as Sector Count                                                    |
|A2h       |Read/Write|ASD PCWHD10/PCWHD20 - Sector Count                                               |Conflicts with Timatic                                                                         |
|A3h       |Write     |AMX Mouse - PPI Mode Register                                                    |Write 93h at startup for basic I/O mode                                                        |
|A3h       |Read/Write|Timatic Winchester / SASI (NCR 5380) - Target Command Register                   |Also used by ASD PCWHD10/20 as Sector Number                                                   |
|A3h       |Read/Write|ASD PCWHD10/PCWHD20 - Sector Number                                              |Conflicts with Timatic                                                                         |
|A4h       |Read/Write|Timatic Winchester / SASI (NCR 5380) - SCSI Bus Status / Select Register         |Also used by ASD PCWHD10/20 as Cylinder Low                                                    |
|A4h       |Read/Write|ASD PCWHD10/PCWHD20 - Cylinder Low                                               |Conflicts with Timatic                                                                         |
|A5h       |Read/Write|Timatic Winchester / SASI (NCR 5380) - Bus and Status Register                   |Also used by ASD PCWHD10/20 as Cylinder High                                                   |
|A5h       |Read/Write|ASD PCWHD10/PCWHD20 - Cylinder High                                              |Conflicts with Timatic                                                                         |
|A6h       |Read      |Electric Studio Light Pen - Position Low 8 Bits                                  |12-bit position counter low byte                                                               |
|A6h       |Read/Write|Multilink Network Interface - Data                                               |Read/write data byte                                                                           |
|A6h       |Read/Write|Timatic Winchester / SASI (NCR 5380) - Start DMA Target Receive / Input Data     |Not used by PCW, also used by ASD PCWHD10/20 as Drive/Head                                     |
|A6h       |Read/Write|ASD PCWHD10/PCWHD20 - Drive / Head                                               |Conflicts with Timatic and Light Pen and Multilink                                             |
|A7h       |Read      |Electric Studio Light Pen - Position High 4 Bits + Retrace Flags                 |Bits 6=V.Retrace, Bit 5=H.Retrace, Bits 3-0=high 4 bits of position                            |
|A7h       |Read/Write|Multilink Network Interface - Data (alternate)                                   |Used alongside A6h                                                                             |
|A7h       |Read/Write|Timatic Winchester / SASI (NCR 5380) - Start DMA Initiator Receive / Reset Parity|Not used by PCW, also used by ASD PCWHD10/20 as Status/Command                                 |
|A7h       |Read/Write|ASD PCWHD10/PCWHD20 - Status / Command                                           |Conflicts with Timatic and Light Pen and Multilink                                             |
|A8h       |Read/Write|Cirtech Gem (XTA) - Data Register                                                |XTA hard drive interface, ATA variant maps A8h-AFh                                             |
|A8h       |Read/Write|Cirtech Gem (ATA) - Data                                                         |ATA variant                                                                                    |
|A9h       |Read      |Cirtech Gem (XTA) - Controller Status                                            |Also: Write=Reset controller                                                                   |
|A9h       |Read/Write|Cirtech Gem (ATA) - Error / Features                                             |ATA variant                                                                                    |
|A9h       |Read      |DKTronics Sound Generator - Read Selected AY-3-8912 Register                     |Read currently selected register                                                               |
|AAh       |Read/Write|Cirtech Gem (XTA) - Controller DIP Switches / Generate Controller-Select Pulse   |Read=DIP switches, Write=select pulse                                                          |
|AAh       |Read/Write|Cirtech Gem (ATA) - Sector Count                                                 |ATA variant                                                                                    |
|AAh       |Write     |DKTronics Sound Generator - Select AY-3-8912 Register                            |Write register number to select it                                                             |
|ABh       |Write     |Cirtech Gem (XTA) - DMA and Interrupt Mask                                       |Not used on PCW                                                                                |
|ABh       |Read/Write|Cirtech Gem (ATA) - Sector Number                                                |ATA variant                                                                                    |
|ABh       |Write     |DKTronics Sound Generator - Write to Selected AY-3-8912 Register                 |Write value to selected register                                                               |
|ACh       |Read/Write|Cirtech Gem (ATA) - Cylinder Low                                                 |ATA variant only                                                                               |
|ADh       |Read/Write|Cirtech Gem (ATA) - Cylinder High                                                |ATA variant only                                                                               |
|AEh       |Read/Write|Cirtech Gem (ATA) - Drive / Head                                                 |ATA variant only                                                                               |
|AFh       |Read/Write|Cirtech Gem (ATA) - Status / Command                                             |ATA variant only                                                                               |
|D0h       |Read      |Kempston Mouse - X Position                                                      |0-255, also readable at D2h                                                                    |
|D1h       |Read      |Kempston Mouse - Y Position                                                      |0-255, also readable at D3h                                                                    |
|D2h       |Read      |Kempston Mouse - X Position (mirror)                                             |Same value as D0h                                                                              |
|D3h       |Read      |Kempston Mouse - Y Position (mirror)                                             |Same value as D1h                                                                              |
|D4h       |Read      |Kempston Mouse - Button State                                                    |Bit 0=Left, Bit 1=Right, 0=pressed                                                             |
|DFh       |Read      |MasterScan Optical Scanner                                                       |Bit 0: 0=light, 1=dark                                                                         |
|E0h       |Read      |Spectravideo Joystick Interface                                                  |Bit 4=Right, Bit 3=Up, Bit 2=Left, Bit 1=Fire, Bit 0=Down                                      |
|E0h       |Read      |Cascade (JoyceStick) Joystick Interface                                          |Bit 7=Fire, Bit 4=Up, Bit 2=Down, Bit 1=Right, Bit 0=Left, conflicts with Spectravideo         |
|E0h       |Read/Write|CPS8256 - DART Channel A Data                                                    |Serial/comms interface                                                                         |
|E1h       |Read/Write|CPS8256 - DART Channel A Control                                                 |                                                                                               |
|E2h       |Read/Write|CPS8256 - DART Channel B Data                                                    |                                                                                               |
|E3h       |Read/Write|CPS8256 - DART Channel B Control / CEN Port Status & Control                     |Also used as CPS8256 CEN port: write 10h to select status mode, bit 5=printer ready            |
|E4h       |Read/Write|CPS8256 - 8253 Counter 0                                                         |Used for baud rate setting (transmit)                                                          |
|E5h       |Read/Write|CPS8256 - 8253 Counter 1                                                         |Used for baud rate setting (receive)                                                           |
|E7h       |Write     |CPS8256 - 8253 Write Mode Word                                                   |Write mode byte here (e.g. 36h or 76h for baud rate)                                           |
|E8h       |Write     |CPS8256 CEN Port - Data Output                                                   |Write character to this port before toggling STROBE via E3h                                    |
|E9h       |Read/Write|ProScan Interface - Base Port                                                    |Interface for Naksha hand scanner / fax                                                        |
|EAh       |Read/Write|ProScan Interface - Fax Device Select (FX1)                                      |Select fax as image source                                                                     |
|EBh       |Read/Write|ProScan Interface - Fax Device Select (FX2)                                      |Select fax (second type) as image source                                                       |
|ECh       |Read/Write|ProScan Interface - Hand Scanner Select                                          |Select hand scanner as image source                                                            |
|EDh       |Read/Write|ProScan Interface - Unknown Device Select                                        |Possibly a second type of hand scanner                                                         |
|EFh       |Read/Write|ProScan Interface - Upper Bound Port                                             |Upper port of ProScan range                                                                    |
|F0h       |Write     |Memory Management - Bank Select for 0000h-3FFFh                                  |PCW paging: bit 7=1, bits 6-0=block number                                                     |
|F1h       |Write     |Memory Management - Bank Select for 4000h-7FFFh                                  |PCW paging                                                                                     |
|F2h       |Write     |Memory Management - Bank Select for 8000h-BFFFh                                  |PCW paging                                                                                     |
|F3h       |Write     |Memory Management - Bank Select for C000h-FFFFh                                  |PCW paging                                                                                     |
|F4h       |Write     |CPC Paging Mode - Lock Register                                                  |Bits lock memory ranges from being read from alternate block, not used by CP/M or LocoScript   |
|F4h       |Read      |Timer Counter                                                                    |Bottom 4 bits: counter incremented by timer interrupt (0-15), reading resets it                |
|F5h       |Write     |Video Controller - Roller-RAM Address                                            |Bits 7-0 specify block and offset / 512                                                        |
|F6h       |Write     |Video Controller - Vertical Scroll Origin                                        |Specifies which Roller-RAM line is at top of screen                                            |
|F7h       |Write     |Video Controller - Display Control                                               |Bit 7=inverse video, Bit 6=screen on/off                                                       |
|F8h       |Write     |System Control Port                                                              |Multi-function: video enable/disable, FDC interrupt mode, boot sequence end (value 0 ends boot)|
|F8h       |Read      |System Control Port - Status                                                     |Bit 6=frame flyback, Bit 5=FDC interrupt pending, Bit 4=60Hz PCW flag                          |
|F9h       |Read      |Prototype Serial Interface (IM6403 UART) - Status Register                       |Only on prototype PCW, not on production hardware                                              |
|FCh       |Read      |PCW8256/8512/9256/10 Dot-Matrix Printer Controller - Error Status                |Returns controller error number                                                                |
|FCh       |Write     |PCW8256/8512/9256/10 Dot-Matrix Printer Controller - Command Port                |Used to send commands during reset, also 00FCh and 01FCh used by PCW9512                       |
|FDh       |Read      |PCW8256/8512/9256/10 Dot-Matrix Printer Controller - Printer Status              |Bit 7=bail bar, Bit 6=command done, Bit 1=busy, Bit 0=fault, also used by PCW9512 at 00FDh     |
|FDh       |Write     |PCW8256/8512/9256/10 Dot-Matrix Printer Controller - Command/Data Port           |Sends printer commands during normal operation                                                 |
|FEh       |Read/Write|LocoLink Parallel Transfer Interface                                             |Bit 1=Data 1 (input) / ACK (output), Bit 0=Data 0 (input) / BUSY (output)                      |
|FEh       |Read/Write|Prototype Serial Interface (IM6403 UART) - Data Register                         |Only on prototype PCW, not on production hardware, conflicts with LocoLink                     |
|FFh       |Read/Write|PCW Linkit Parallel Transfer Interface                                           |Two-bit communication channel, value read is binary inverse of value written by other PCW      |

The above information is derived from John Elliott's excellent [[https://www.seasip.info/Unix/Joyce/hardware.pdf|PCW Hardware manual]]. Please note that the hard drive, and SCA Mark 2 Interface information have not been verified.