Zipplet's Stuff

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Supervisor PIC details of operation (PIC16F877A)
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Signal lines
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The Parallel Slave Port is used in microprocessor bus mode to interface
directly to the Z80 bus.

RD0-7: Data bus               -> Z80 data bus
RE0: /Read                    -> Z80 /RD
RE1: /Write                   -> Z80 /WR
RE2: /select                  -> I/O address decoder pin 2 ($20-$2F)
RA0: /IRQ line                -> Z80 /IRQ

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Packet format
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| Byte | Length | Description                                                   |
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| 0    | 1      | Command word                                                  |
| 1    | 1      | Length of data (0-255)                                        |
| 2    | n/a    | Data / parameters                                             |
---------------------------------------------------------------------------------

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CPU -> PIC commands
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$00 - RESET ALL
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Causes the supervisor to reset to the power on state. The supervisor will respond with a $00 - RESET ACK packet.

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PIC -> CPU responses and commands
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$00 - RESET ACK
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Sent to the CPU as a response to $00 - RESET ALL.
The data bytes contain a human readable chip ID/version string.