Jameco Electronics Rabbit 3000 - Manual (Page 215)

206 Rabbit 3000 Microprocessor
Bits 1,0—This 2-bit field sets the priority of the slave port interrupt. The interrupt is disabled
by (0,0).
Table 13-3 describes the slave port status register. The status register has 6 bits that are set if
the particular register is full. That means that the register has been written by the processor that
can write to it but it has not been read by the processor that can read it. The bits for SPD0R are
used to control the slave interrupt and the handshaking lines as shown in Figure 13-3.
13.3 Applications and Communications Protocols for Slaves
The communications protocol used with the slave port depends on the application. A slave
processor may be used for various reasons. Some possible applications are listed below.
Keep in mind that the Rabbit can also be operated as a slave processor via a serial port and
some of the protocols will work well via a serial communications connection. If a serial
connection is used, the protocol becomes more complicated if errors in transmission need
to be taken into account. If the physical link can be controlled so that transmission errors
do not occur, a realistic possibility if the interconnection environment is controlled, the
serial protocol is simpler and faster than if error correction needs to be taken into account.
13.3.1 Slave Applications
• Motion Controller—Many types of motion control require fast action, may be com-
pute-intensive or both. Traditional servo system solutions may be overly expensive or
not work very well because of system nonlinearities. The basic communications model
for a motion controller is for the master to send short messages—positioning com-
mands—to the slave. The slave acknowledges execution of the commands and reports
exception conditions.
• Communications Protocol Processor—Communications protocols may be very com-
plex, may require fast responses, or may be compute-intensive.
• Graphics Controller—The Rabbit can be used to perform operations such as drawing
geometric figures and generating characters.
• Digital Signal Processing—Although the Rabbit is not a speciality digital signal pro-
cessor, it has enough compute speed to handle some types of jobs that might otherwise
Table 13-3. Slave Port Status Register (SPSR) (adr = 0x023)
Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
1—set by
master
write to
SPD0R.
Cleared by
slave write
to SPSR.
1—set by
master
write to
SPD2R.
Cleared
when slave
reads
register. 1—set by
master
write to
SPD1R.
Cleared
when slave
reads
register. 1—set by
master
write to
SPD0R.
Cleared
when slave
reads
register.
1—set by
slave write
to SPD0R.
Cleared by
master
write to
SPSR.
1—set by
slave write
to SPD2R.
Cleared
when
master
reads
register. 1—set by
slave write
to SPD1R.
Cleared
when
master
reads
register.
1—set by
slave
write to
SPD0R.
Cleared
when
master
reads
register.