SAM7S256_14 Datasheet, PDF (417/775 Pages) ATMEL Corporation – ARM-based Flash MCU

32.6.5 Frame Sync
The Transmitter and Receiver Frame Sync pins, TF and RF, can be programmed to generate different kinds of
frame synchronization signals. The Frame Sync Output Selection (FSOS) field in the Receive Frame Mode Regis-
ter (SSC_RFMR) and in the Transmit Frame Mode Register (SSC_TFMR) are used to select the required
waveform.
• Programmable low or high levels during data transfer are supported.
• Programmable high levels before the start of data transfers or toggling are also supported.
If a pulse waveform is selected, the Frame Sync Length (FSLEN) field in SSC_RFMR and SSC_TFMR programs
the length of the pulse, from 1 bit time up to 16 bit time.
The periodicity of the Receive and Transmit Frame Sync pulse output can be programmed through the Period
Divider Selection (PERIOD) field in SSC_RCMR and SSC_TCMR.
32.6.5.1 Frame Sync Data
Frame Sync Data transmits or receives a specific tag during the Frame Sync signal.
During the Frame Sync signal, the Receiver can sample the RD line and store the data in the Receive Sync Hold-
ing Register and the transmitter can transfer Transmit Sync Holding Register in the Shifter Register. The data
length to be sampled/shifted out during the Frame Sync signal is programmed by the FSLEN field in
SSC_RFMR/SSC_TFMR and has a maximum value of 16.
Concerning the Receive Frame Sync Data operation, if the Frame Sync Length is equal to or lower than the delay
between the start event and the actual data reception, the data sampling operation is performed in the Receive
Sync Holding Register through the Receive Shift Register.
The Transmit Frame Sync Operation is performed by the transmitter only if the bit Frame Sync Data Enable
(FSDEN) in SSC_TFMR is set. If the Frame Sync length is equal to or lower than the delay between the start event
and the actual data transmission, the normal transmission has priority and the data contained in the Transmit Sync
Holding Register is transferred in the Transmit Register, then shifted out.
32.6.5.2 Frame Sync Edge Detection
The Frame Sync Edge detection is programmed by the FSEDGE field in SSC_RFMR/SSC_TFMR. This sets the
corresponding flags RXSYN/TXSYN in the SSC Status Register (SSC_SR) on frame synchro edge detection (sig-
nals RF/TF).
32.6.6 Receive Compare Modes
Figure 32-12. Receive Compare Modes
RK
RD
(Input)
CMP0 CMP1 CMP2 CMP3
Start
Ignored
B0
B1
B2
FSLEN
Up to 16 Bits
(4 in This Example)
STDLY
DATLEN
32.6.6.1 Compare Functions
Length of the comparison patterns (Compare 0, Compare 1) and thus the number of bits they are compared to is
defined by FSLEN, but with a maximum value of 16 bits. Comparison is always done by comparing the last bits
received with the comparison pattern. Compare 0 can be one start event of the Receiver. In this case, the receiver
SAM7S Series [DATASHEET]
6175M–ATARM–26-Oct-12
417