SYNCHRONOUS SERIAL INTERFACE (SSI)
MOTOROLA
PORT C
6 - 91
6.4.2.2.7
CRB Shift Direction (SHFD) Bit 6
This bit causes the transmit shift register to shift data out MSB first when SHFD equals
zero or LSB first when SHFD equals one. Receive data is shifted in MSB first when SHFD
equals zero or LSB first when SHFD equals one. Hardware reset and software reset clear
SHFD.
6.4.2.2.8
CRB Frame Sync Length (FSL0 and FSL1) Bits 7 and 8
These bits select the type of frame sync to be generated or recognized (see Table 6-11).
If FSL1 equals zero and FSL0 equals zero, a word-length frame sync is selected for both
TX and RX that is the length of the data word defined by bits WL1 and WL0. If FSL1 equals
one and FSL0 equals zero, a 1-bit clock period frame sync is selected for both TX and RX.
When FSL0 equals one, the TX and RX frame syncs are different lengths. Hardware reset
and software reset clear FSL0 and FSL1.
Table 6-11 Frame Sync Length
6.4.2.2.9
CRB Sync/Async (SYN) Bit 9
SYN controls whether the receive and transmit functions of the SSI occur synchronously
or asynchronously with respect to each other. When SYN is cleared, asynchronous mode
is chosen and separate clock and frame sync signals are used for the transmit and receive
sections. When SYN is set, synchronous mode is chosen and the transmit and receive
sections use common clock and frame sync signals. Hardware reset and software reset
clear SYN.
6.4.2.2.10
CRB Gated Clock Control (GCK) Bit 10
GCK is used to select between a continuously running data clock or a clock that runs only
when there is data to be sent in the transmit shift register. When GCK is cleared, a con-
tinuous clock is selected; when GCK is set, the clock will be gated. Hardware reset and
software reset clear GCK.
Note: For gated clock mode with externally generated bit clock, internally generated
frame sync is not defined.
FSL1
FSL0
Frame Sync Length
0
0
WL bit clock for both TX/RX
0
1
One-bit clock for TX and WL bit clock for RX
1
0
One-bit clock for both TX/RX
1
1
One-bit clock for RX and WL bit clock for TX
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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