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 2-3shows the data paths in the slave port.

 

Rabbit 3000

 

Master

Input Register

CPU

Processor

 

 

 

Output Registers

 

Control

Slave Interface Registers

 

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.

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Rabbit 3000 Microprocessor

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Jameco Electronics 2000, 3000 manual Slave Port, Rabbit