ADSP-21368 SHARC Processor Hardware Reference 5-37
Serial Ports
Frame Sync Options
Framing signals indicate the beginning of each serial word transfer. A vari-
ety of framing options are available on the SPORTs. The SPORTx_FS
signals are independent and are separately configured in the control
register.
Framed Versus Unframed Frame Syncs
The use of frame sync signals is optional in SPORT communications. The
FSR (transmit frame sync required) control bit determines whether frame
sync signals are required. Active low or active high frame syncs are selected
using the LFS bit. This bit is located in the SPCTLx control registers.
When FSR is set (=1), a frame sync signal is required for every data word.
To allow continuous transmission from the processor, each new data word
must be loaded into the transmit buffer before the previous word is shifted
out and transmitted.
When FSR is cleared (=0), the corresponding frame sync signal is not
required. A single frame sync is required to initiate communications but it
is ignored after the first bit is transferred. Data words are then transferred
continuously in what is referred to as an unframed mode.
L
When DMA is enabled in a mode where frame syncs are not
required, DMA requests may be held off by chaining or may not be
serviced frequently enough to guarantee continuous unframed data
flow.
Figure 5-7 illustrates framed serial transfers.
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