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54
Rabbit 2000 Microprocessor
I/O Read
Strobe
/IORD
Output
I/O read strobe. Driven low on an external
I/O read bus cycle. May be used to drive
glue logic concerned with I/O expansion,
such as the direction pin on a bidirectional
bus buffer. See also programmable strobes
in port E.
32
I/O Write
Strobe
/IOWR
Output
I/O write strobe. Driven low as a write
strobe during external I/O write cycles. Is
enabled by the I/O bank control register.
See also programmable strobes in port E.
31
I/O Port A
PA0–PA7
Input/
Output
These 8 bits serve as general-purpose input
output or they serve as the data port for the
slave port. On reset these pins are set to
inputs and they float.
81–88
I/O Port B
PB0–PB7
6 In/2 Out
I/O Port B. When used as parallel I/O, PB7
and PB6 are outputs only. PB0–PB5 are
inputs only.
PB0 and PB1 can be outputs when set up as
the clock for the clocked serial ports. On
reset, the outputs are set to zero. If the
slave port is enabled, the following
alternate assignments apply:
PB7—/SLAVEATTN: slave requests
attention.
PB5, PB4—address lines (SA1, SA0) for
slave registers.
PB3—slave negative read strobe from
master.
PB2—slave negative write strobe from
master.
If serial port A is enabled in clocked mode,
then PB1 is the bidirectional clock line. If
serial port B is enabled in clocked mode,
then PB0 is the bidirectional clock line.
93–100
I/O Port C
PC0–PC7
4 In/4 Out
I/O Port C. When used as a parallel port,
bits 1, 3, 5, 7 are inputs and bits 0, 2, 4, 6
are outputs. Bits 0, 2, 4, 6 can alternately be
selectively enabled to serve as the serial
data output for serial ports D, C, B, A
respectively. Bits 1, 3, 5, 7 serve as the
serial data inputs for serial ports D, C, B,
A. These inputs can also be read from the
parallel port register when they are being
used by the serial port UART.
51, 54–60
Table 5-1. Rabbit Pin Descriptions (continued)
Pin Group
Pin Name
Direction
Function
Pin Numbers
Summary of Contents for 2000
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