Used The Zilog [[Z80 PIO]] chip (aka Z84C20) is a '''Dual 8bit''' I/O Port (not to be confused with the '''Triple 8bit''' [[8255 PPI chip]], which is sometimes referred to as PIO, too). == Register Addressing == The chip has B/A (Port B/A Select) and C/D (Control/Data Select) pins, which may be connected to the CPUs A0 and A1 pins (or vice-versa, A1 and A0) (or other pins like A3 and A4). Anyways, no matter how the addressing is done: There are 4 registers - 2 Data registers, and 2 Control registers. == Data Registers A and B == Data direction can be configured in the corresponding control register. Depending on the direction, the data bits are inputs or outputs with following meaning: 7-0 Data (0=Low, 1=High)Aside from the 8 data lines, each port additionaly supports automatic /STROBE and READY handshaking signals (whereas, unlike as in printer ports, STROBE can act as an input, not an output), the handshaking stuff isn't used in Mode3. == Control Registers A and B == When D0=0: 7-1 Interrupt Vectors Bit7-1 (Vector Bit0 is fixed = zero) 0 Must be 00hWhen D0..D3=03h: 7 Interrupt Enable (1=Enable) (same as when D0..D3=0Fh) 6-4 Not used (should be zero) 0-3 Must be 03hWhen D0..D3=07h: 7 Interrupt Enable (1=Enable) 6 Interrupt AND/OR (0=OR, 1=AND) ;\ 5 Interrupt High Low (1=High) ; used in Mode3 only 4 Interrupt Mask Follows ;/ ;<--- also ACK interrupt? 0-3 Must be 07hWhen D0..D3=0Fh: 7-6 Mode (0=out, 1=in, 2=bidirectional,3=control) (mode2 on PortA only) 5-4 Not used (should be zero) 0-3 Must be 0FhAfter Mode3 (control mode) was set, then next control write is: 0-7 Direction bits, separately for each pin (0=out, 1=in)After InterruptMaskFollows was set (in Mode3 only?), then next write is: 0-7 Select bits to be monitored (in OR mode: 0=Select) == Usage in CPC == A [[Z80 PIO]] is used by the following CPC hardware expansions: * [[ACU Real Time Clock (DIY)]]* [[Dk'tronics Real Time Clock]]* [[PDS development system]] == Datasheet == * [[Media:Z80pio z84c20.pdf]] - Zilog Z80 PIO Datasheet [[Category:Programming]][[Category:CPC Internal Components]][[Category:Electronic Component]]
