Jameco Electronics Rabbit 3000 - Manual (Page 23)

14 Rabbit 3000 Microprocessor
2.2.6 Slave Port
The slave port is designed to allow the Rabbit to be a slave to another processor, which
could be another Rabbit. The port is shared with Parallel Port A and is a bidirectional data
port. The master can read any of three registers selected via two select lines that form the
register address and a read strobe that causes the register contents to be output by the port.
These same registers can be written as I/O registers by the Rabbit slave. Three additional
registers transmit data in the opposite direction. They are written by the master by means
of the two select lines and a write strobe.
Figure 2-3 shows the data paths in the slave port.
Figure 2-3. Slave-Port Data Paths
The slave Rabbit can read the same registers as I/O registers. When incoming data bits are
written into one of the registers, status bits indicate which registers have been written, and
an optional interrupt can be programmed to take place when the write occurs. When the
slave writes to one of the registers carrying data bits outward, an attention line is enabled
so that the master can detect the data change and be interrupted if desired. One line tells
the master that the slave has read all the incoming data. Another line tells the master that
new outgoing data bits are available and have not yet been read by the master. The slave
port can be used to signal the master to perform tasks using a variety of communication
protocols over the slave port.
CPU
Master
Processor
Slave Interface Registers
Input Register
Output Registers
Control
Rabbit 3000