Slave Port; Overview - Rabbit 6000 User Manual

21.1 Overview

The slave port is a parallel communication port that can be used to communicate with an external master
device. The slave port consists of three data input and data output registers, and a status register.
The data input registers are written by the master (the external device) and are read by the slave. The data
output registers are written by the slave and are read by the master. Note that the data registers are named
from the point of view of the slave. The slave device can only read the data input registers and write to the
data output registers. Similarly, the master device can only read the data input registers and write the data
output registers. Both devices can read and write to the status register.
The status register contains the interrupt status bits and a status flag corresponding to each data input or
data output register to indicate the empty or full status of the data register. Data registers are marked full
when written by the source side of the interface, and are marked empty when read by the destination side
of the interface.
The hardware interface to the external master consists of an 8-bit bidirectional data bus with a read strobe,
write strobe, and chip select. There are two address lines that select one of the three data registers or the
status register.
A slave attention signal is asserted when the slave writes to its SPD0R and can be deasserted by the master
by performing a dummy write to the status register. This signal can be used to interrupt the master to indi-
cate that the master needs to read data from the slave.
The slave port interrupt is asserted when the master writes to SPD0R. The slave clears this interrupt condi-
tion by writing to the status register.
The slave port can be used to bootstrap the processor by setting the SMODE pins appropriately. See
Chapter 3 for more information on this mode.
If a Rabbit is used as the master device as well as the slave, the recommended bus interface for the master
to use is the External I/O bus.
Rabbit 6000 User's Manual
Table 21-1. Slave Port Addresses
Slave Port Address
00
01
10
11
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21. S
Slave Port Register
Data Register 0
Data Register 1
Data Register 2
Status Register
P
LAVE ORT
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