SYNCHRONOUS SERIAL INTERFACE (SSI)
6 - 146
PORT C
MOTOROLA
Initializing the on-demand mode for the example illustrated in Figure 6-81 is accomplished
by setting the bits in CRA and CRB as follows:
1.
The word length must be selected by setting WL1 and WL0. In this example, a
24-bit word length was chosen (WL1=1 and WL0=1).
2.
The on-demand mode is selected by clearing DC4–DC0.
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 gated clock (GCK=1) is selected in this example. A continuous clock exam-
ple is shown in Figure 6-78.
7.
Asynchronous clock control was selected (SYN=0) in this example.
8.
Since gated clock is used, the frame sync is not necessary. FSL1 and FSL0
can be ignored.
9.
SCKD must be an output (SCKD=1).
10.
SCD0 must be an input (SCD0=0).
11.
Control bit SHFD should be set as needed for the application. Pins SC1 and
SC2 are undefined in this mode (see Table 6-13) and should be programmed
as general-purpose I/O pins.
DSP56002
DSP1
STD
SCK
SRD
SC0
DSP56002
DSP2
SRD
SCO
STD
SCK
Figure 6-80 On Demand Example
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Freescale Semiconductor, Inc.
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