Download DSP56002 User`s Manual Rev. 1

SYNCHRONOUS SERIAL INTERFACE (SSI)
23
X:$FFE1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
CC CC CC CC CC CC CC CC CC
8 7 6
5
4 3
2
1
0
STD
SCK
SRD
CCx
GPIO
1
Serial Interface
C
SC1
SC0
Function
0
P
O
R
T
SC2
PORT C CONTROL
REGISTER (PCC)
PC0
PC1
PC2
SC0
SC1
SC2
SCK
SRD
STD
SERIAL CONTROL PIN 0
SERIAL CONTROL PIN 1
SERIAL CONTROL PIN 2
SERIAL CLOCK PIN
SERIAL RECEIVE DATA PIN
SERIAL TRANSMIT DATA PIN
Figure 6-52 SSI Initialization Procedure
Figure 6-52 shows the six control bits in the PCC, which select the six SSI pins as either
general-purpose I/O or as SSI pins. The STD pin can only transmit data; the SRD pin can
only receive data. The other four pins can be inputs or outputs, depending on how they
are programmed. This programming is accomplished by setting bits in CRA and CRB as
shown in Figure 6-46. The CRA (see Figure 6-50) sets the SSI bit rate clock with PSR and
PM0–PM7, sets the word length with WL1 and WL0, and sets the number of words in a
frame with DC0–DC4. There is a special case where DC4–DC0 equals zero (one word
per frame). Depending on whether the normal or network mode is selected (MOD=0 or
MOD=1, respectively), either the continuous periodic data mode is selected, or the on-demand data driven mode is selected. The continuous periodic mode requires that FSL1
equals one and FSL0 equals zero. Figure 6-51 shows the meaning of each individual bit
in the CRB. These bits should be set according to the application requirements.
Table 6-15 (a) and Table 6-15 (b) provide a convenient listing of PSR and PM0–PM7 settings for the common data communication rates and the highest rate possible for the SSI
for the chosen crystal frequencies. The crystal frequency selected for Table 6-15 (a) is the
one used by the DSP56002ADS board; the one selected for Table 6-15 (b) is the closest
one to 40 MHz that divides down to exactly 128 kHz. If an exact baud rate is required, the
crystal frequency may have to be selected. Table 6-16 gives the PSR and PM0–PM7 settings in addition to the required crystal frequency for three common telecommunication frequencies.
MOTOROLA
PORT C
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