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#### 9.2.2.8 TPI module

The TPI 6525 is a chip with three I/O ports (Tri-Port-Interface). One of the ports can double as an interrupt prioritizer. Therefore we also have to save the states of the interrupt stack etc.

Version numbers: Major 1, Minor 0.

Type | Name | Description
BYTE | PRA | Port A output register
BYTE | PRB | Port B output register
BYTE | PRC | Port C output register (doubles as IRQ latch register)
BYTE | DDRA | Port A data direction register
BYTE | DDRB | Port B data direction register
BYTE | DDRC | Port C data direction register (doubles as IRQ mask register)
BYTE | CR | Control Register
BYTE | AIR | Active interrupt register
BYTE | STACK | Interrupt stack - the interrupt bits that are not (yet) served.
BYTE | CABSTATE | State of CA/CB pins. Bit 7 = state of CA, Bit 6 = state of CB