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11.3.7.5 Unexpected Transmit Frame Synchronization: XSYNCERR
Figure 11–31. Response to Transmit Frame Synchronization
Figure 11–26 shows the decision tree that the transmitter uses to handle all
incoming frame synchronization signals. The diagram assumes that the trans-
mitter has been started (XRST = 1). An unexpected transmit frame sync pulse
is defined as a sync pulse that occurs XDATDLY bit clocks earlier than the last
transmitted bit of the previous frame. Any one of three cases can occur:
Case 1: Unexpected FSX pulses with XFIG = 1. This case is discussed in
section 11.3.6.1 and shown in Figure 11–21. In this case, unexpected FSX
pulses are ignored, and the transmission continues.
Case 2: FSX pulses with normal serial port transmission. This situation is
discussed in section 11.3.5.3. There are two possible reasons for a trans-
mit not to be in progress:
J
This FSX pulse is the first one to occur after XRST = 1.
J
The serial port is in the interpacket intervals. The programmed data
delay (XDATDLY) may start during these interpacket intervals before
the first bit of the next element is transmitted. Thus, if operating at
maximum packet frequency, frame synchronization can still be re-
ceived XDATDLY bit clocks before the first bit of the associated ele-
ment.
Transmit frame
sync pulse occurs.
Unexpected
frame sync
XFIG = 1 ?
Case 1:
Ignore frame pulse.
Transmitter continues running.
No
pulse ?
Yes
No
Yes
Multichannel Buffered Serial Ports
Data Transmission and Reception
Case 2:
Normal transmission
Start new transmit.
Case 3:
Abort transfer.
Set XSYNCERR.
Restart current transfer.
11-47
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