Frame Sync Options; Framed Versus Unframed Frame Syncs - Analog Devices ADSP-21261 SHARC Hardware Reference Manual

Frame Sync Options

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
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 serial port communications.
The (transmit frame sync required) control bit determines whether
FSR
frame sync signals are used. Active low or high frame syncs are selected
using the bit. This bit is located in the
LFS
When is set (=1), a frame sync signal is required for every data word.
FSR
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 is cleared (=0), the corresponding frame sync signal is not
FSR
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.
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 fre-
quently enough to guarantee continuous unframed data flow.
Figure 9-6 illustrates framed serial transfers.
9-34 ADSP-2126x SHARC Processor Hardware Reference
SPORTx_FS
control registers.
SPCTLx