Rabbit 6000 User’s Manual
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31.2 Dependencies
31.2.1 I/O Pins
The external I/O bus uses PA0–PA7 for the lower byte of data, and PH0–PH7 for the upper byte if 16-bit
mode is enabled in IBxER. All Parallel Port H settings are overridden if the 16-bit I/O bus mode is
enabled.
Either PB2–PB7 or PB0–PB7 are used for address lines, depending on the setting in SPCR. Address bits 6
and 7 can also be enabled on pins PD1, PD3, PD5, or PD7, which allows PB0 and PB1 to be used as
clocked serial I/O instead of as external I/O.
The /IOWR, /IORD, and /BUFEN pins are dedicated strobes for external I/O accesses. Drive strength,
slew rate, and the pullup/down resistor status are selectable via IOPCR.
The I/O strobes can be directed to pins on Parallel Ports C, D, E, F, G, or H; each bank can be directed to
the appropriate pin (bank zero on PC0, PD0, or PE0; bank one on PC1, PD1, or PE1; etc.). The settings for
each strobe will be reflected on /IOWR, /IORD, and /BUFEN as well whenever that bank is accessed.
The I/O handshake can be input on any one of the Parallel Port E pins (PE0–PE7).
31.2.2 Clocks
All external I/O accesses, strobes, and handshake timeouts are based on the processor clock, which can be
taken directly or divided by 2, 4, 8, or 16 separately for each IO bank in the appropriate IBxER to provide
slower access times when the main clock is at a high frequency. This is independent of the number of wait
states which can also be programmed. Note that this divider setting is ignored when the processor clock is
set to run off the 32 kHz clock.
31.2.3 Other Registers
31.2.4 Interrupts
There are no interrupts associated with external I/O.
Register
Function
SPCR
Enable the external I/O bus.
PCFR, PCALR, PCAHR
PDFR, PDALR, PDAHR,
PEFR, PEALR, PEAHR
PFFR, PFALR, PFAHR
PGFR, PGALR, PGAHR
PHFR, PHALR, PHAHR
Select Parallel Port pins as I/O strobe outputs.
Select PD1, PD3, PD5, or PD7 as address bits
6–7.
Summary of Contents for 6000
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