Frame Sync Options - Analog Devices ADSP-2106x SHARC User Manual

10 Serial Ports
10.6

FRAME SYNC OPTIONS

Framing signals indicate the beginning of each serial word transfer.
The framing signals for each serial port are TFS (transmit frame
synchronization) and RFS (receive frame synchronization). A variety of
framing options are available; these options are configured in the serial
port control registers. The TFS and RFS signals of a serial port are
independent and are separately configured in the control registers.
10.6.1 Framed vs. Unframed
The use of frame sync signals is optional in serial port
communications. The TFSR (transmit frame sync required) and RFSR
(receive frame sync required) control bits determine whether frame
sync signals are required. These bits are located in the the STCTLx and
SRCTLx control registers.
When TFSR=1 or RFSR=1, a frame sync signal is required for every
data word. To allow continuous transmitting from the ADSP-2106x,
each new data word must be loaded into the TX buffer before the
previous word is shifted out and transmitted. (See "Data-Independent
Frame Syncs" in this chapter.)
When TFSR=0 or RFSR=0, the corresponding frame sync signal is not
required. A single frame sync is needed to initiate communications but
is ignored after the first bit is transferred. Data words are then
transferred continuously, unframed. (Caution: When DMA is enabled
in this mode, with frame syncs not required, DMA requests may be
held off by chaining or may not be serviced frequently enough to
guarantee continuous unframed data flow.)
Figure 10.6 illustrates framed serial transfers, which have the following
characteristics:
• TFSR and RFSR bits in STCTLx, SRCTLx control registers
determine framed or unframed mode.
• Framed mode requires a framing signal for every word. Unframed
mode ignores framing signal after first word.
• Unframed mode is appropriate for continuous reception.
• Active-low or active-high frame syncs selected with LTFS and LRFS
bits of STCTLx, SRCTLx control registers.
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