SERIAL COMMUNICATION INTERFACE (SCI)
6 - 74
PORT C
MOTOROLA
6.3.11
Example Circuits
The SCI can be used in a number of configurations to connect multiple processors. The
synchronous mode shown in Figure 6-39 shows the DSP acting as a slave. The 8051 pro-
vides the clock that clocks data in and out of the SCI, which is possible because the SCI
shift register mode timing is compatible with the timing for 8051/8096 processors. Trans-
mit data is changed on the negative edge of the clock, and receive data is latched on the
positive edge of the clock. A protocol must be used to prevent both processors from trans-
mitting simultaneously. The DSP is also capable of being the master device.
A multimaster system can be configured (see Figure 6-41) using a single transmit/receive
line, multidrop word format, and wired-OR. The use of wired-OR requires a pullup resistor
as shown. A protocol must be used to prevent collisions. This scheme is physically the
simplest multiple DSP interconnection because it uses only one wire and one resistor.
The master-slave system shown in Figure 6-40 is different in that it is full duplex. The clock
pin is not required; thus, it is configured as a GPIO pin. Communication is asynchronous.
The slave’s transmitters must be wire-ORed because more than one transmitter is on one
line. The master’s transmitter does not need to be wire-ORed.
CLOCK INPUT
TRANSMIT DATA
RECEIVE DATA
1.5 C
cyc
B0
B1
B2
B3
B4
B5
B6
B7
XXXXXX
XX
XX
XX
XX
XX
XX
XX
XXXXXXX
SAMPLE
0
1
2
3
4
5
6
7
DSP56002
8051
RXD
TXD
SCLK
P3.0
P3.1
Figure 6-39 Synchronous Mode Example
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