MOTOROLA
Chapter 30. Serial Management Controllers
30-23
Part V. The Communications Processor Module
Note that regardless of whether the transmitter or receiver uses SMSYN, it must make
glitch-free transitions from high-to-low or low-to-high. Glitches on SMSYN can cause
erratic behavior of the SMC.
The transmitter and receiver never lose synchronization again, regardless of the state of
SMSYN, until the TEN bit is cleared or an
ENTER
HUNT
MODE
command is issued.
Figure 30-11. Synchronization with SMSYNx
If both SMCMR[REN] and SMCMR[TEN] are set, the Þrst falling edge of SMSYN causes
both the transmitter and receiver to achieve synchronization. The SMC transmitter can be
disabled and reenabled and SMSYN can be used again to resynchronize the transmitter
itself. Section 30.2.4, ÒDisabling SMCs On-the-Fly,Ó describes how to safely disable and
reenable the SMC. Simply clearing and setting TEN may be insufÞcient. The receiver can
also be resynchronized this way.
30.4.6 Using TSA for Synchronization
The TSA offers an alternative to using SMSYN to internally synchronize the SMC channel.
This method is similar, except that the synchronization event is the Þrst time-slot for this
SMC receiver/transmitter after the frame sync indication rather than the falling edge of
SMCLK
SMSYN
SMTXD
1s are sent
Five 1s are sent
TEN set
here
Tx FIFO
loaded
approximately
here
Five 1s
assume
character
length
equals 5
First bit of
Þrst 5-bit
transmit
character
(lsb)
Transmission
could begin
here if Tx FIFO
not loaded
in time
SMSYN
detected
low here
SMCLK
SMSYN
SMRXD
REN set
here or
First bit
of receive
data
(lsb)
SMSYN
detected
low here
ENTER
HUNT
MODE
command
issued
NOTES:
SMCLK is an internal clock derived from an external
CLK
x
or a baud rate generator.
1.
This example shows the SMC receiver and transmitter
2.
enabled separately. If the REN and TEN bits were set at
the same time, a single falling edge of SMSYN would
synchronize both.
SMC1 Transmit Data
SMC1 Receive Data
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