SYNCHRONOUS SERIAL INTERFACE (SSI)
6 - 138
PORT C
MOTOROLA
The receiver operates in a similar manner. When the receiver is full, an interrupt is gen-
erated, and a test is made to see if this is the beginning of a frame. If it is the beginning of
a frame, SLOTCT2 is cleared to start counting the time slots. If it is not the beginning of a
frame, SLOTCT2 is incremented. The next test checks to see if the data received is in-
tended for this DSP. If the current time slot is the one assigned to the DSP receiver, the
data is kept; otherwise, the data is discarded, and the DSP can then return to what it was
doing before the interrupt. SLOTCT2 should reflect the data in the receive shift register to
coincide with the RFS flag. Software must recognize that the data being read from RX is
for time slot SLOTCT2 minus two.
Initializing the network mode is accomplished by setting the bits in CRA and CRB as fol-
lows (see Figure 6-77):
1. The word length must be selected by setting WL1 and WL0. In this example,
an 8-bit word length was chosen (WL1=0 and WL0=0).
2. The number of time slots is selected by setting DC4–DC0. Four time slots
were chosen for this example (DC4–DC0=$03).
3. The serial clock rate must be selected by setting PSR and PM7–PM0 (see
Table 6-15 (a), Table 6-15 (b), and Table 6-16).
4. RE and TE must be set to activate the transmitter and receiver. If interrupts
are to be used, RIE and TIE should be set. RIE and TIE are usually set after
everything else is configured and the DSP is ready to receive interrupts.
5. The network mode must be selected (MOD=1).
6. A continuous clock is selected in this example by setting GCK=0.
7. Although it is not required for the network mode, synchronous clock control
was selected (SYN=1).
8. The frame sync length was chosen in this example as word length (FSL1=0)
for both transmit and receive frame sync (FSL0=0). Any other combinations
could have been selected, depending on the application.
9. Control bits SHFD, SCKD, SCD2, SCD1, SCD0, and the flag bits (OF1 and
OF0) should be set as needed for the application.
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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