A0
Current data retransmitted
New data received
(R/X)SYNCERR
DX
C6
C7
B0
B1
B2
B3
B4
B5
B6
B7
B6
B7
A0
DR
FS(R/X)
D6
D7
C0
C2
C3
C4
C5
C6
C7
B6
B7
C1
CLK(R/X)
Frame sync aborts current transfer
Architecture
1213
SPRUH82C – April 2013 – Revised September 2016
Copyright © 2013–2016, Texas Instruments Incorporated
Multichannel Buffered Serial Port (McBSP)
25.2.7.4 Frame Synchronization Ignore
The McBSP can be configured to ignore transmit and receive frame synchronization pulses. The (R/X)FIG
bit in (R/X)CR can be cleared to 0 to recognize frame sync pulses, or it can be set to 1 to ignore frame
sync pulses. In this way, you can use (R/X)FIG either to pack data, if operating at maximum frame
frequency, or to ignore unexpected frame sync pulses.
25.2.7.4.1 Frame Sync Ignore and Unexpected Frame Sync Pulses
RFIG and XFIG are used to ignore unexpected internal or external frame sync pulses. Any frame sync
pulse is considered unexpected if it occurs one or more bit clocks earlier than the programmed data delay
from the end of the previous frame specified by ((R/X)DATDLY). Setting the frame ignore bits to 1 causes
the serial port to ignore these unexpected frame sync signals.
In reception, if not ignored (RFIG = 0), an unexpected FSR pulse discards the contents of RSR in favor of
the incoming data. Therefore, if RFIG = 0, an unexpected frame synchronization pulse aborts the current
data transfer, sets RSYNCERR in SPCR to 1, and begins the reception of a new data element. When
RFIG = 1, the unexpected frame sync pulses are ignored.
In transmission, if not ignored (XFIG = 0), an unexpected FSX pulse aborts the ongoing transmission, sets
the XSYNCERR bit in SPCR to 1, and reinitiates transmission of the current element that was aborted.
When XFIG = 1, unexpected frame sync signals are ignored.
shows that element B is interrupted by an unexpected frame sync pulse when (R/X)FIG = 0.
The reception of B is aborted (B is lost), and a new data element (C) is received after the appropriate data
delay. This condition causes a receive synchronization error and thus sets the RSYNCERR bit. However,
for transmission, the transmission of B is aborted and the same data (B) is retransmitted after the
appropriate data delay. This condition is a transmit synchronization error and thus sets the XSYNCERR
bit. Synchronization errors are discussed in
and
.
Figure 25-19. Unexpected Frame Synchronization With (R/X)FIG = 0