
Serial Management Controllers (SMCs)
7-294
MC68360 USER’S MANUAL
NOTE
Regardless of whether the transmitter or receiver uses the SM-
SYNx signal, the SMSYNx signal must make glitch-free transi-
tions from high to low or low to high. Glitches on SMSYNx may
cause errant behavior of the SMC.
Once the REN bit is set in SMCMR, the first rising edge of SMCLK that detects the SMSYNx
pin as low causes the SMC receiver to achieve synchronization. Data will begin to be
received (latched) on the same rising edge of SMCLK that latched SMSYNx. This will be the
first bit of data received. The receiver will never lose synchronization again, regardless of
the state of SMSYNx, until the REN bit is cleared by the user.
Figure 7-78. Synchronization with the SMSYNx Pin
Once the TEN bit is set in SMCMR, the first rising edge of SMCLK that detects the SMSYNx
pin as low causes the SMC transmitter to achieve synchronization. The SMC transmitter will
begin transmitting ones asynchronously from the falling edge of SMSYNx. After one char-
acter of ones is transmitted, if the transmit FIFO is loaded (i.e., the Tx BD was ready with
SMRXD
SMC1 RECEIVE DATA
SMTXD
SMSYN
SMCLK
TEN
SET
HERE
TX FIFO
LOADED
APPX.
HERE
SMSYN
DETECTED
LOW HERE
SMCLK
SMSYN
REN SET
HERE OR
ENTER
HUNT MODE
COMMAND
ISSUED
FIRST BIT OF
RECEIVE
DATA (LSB)
1's ARE SENT
SMSYN
DETECTED
LOW HERE
SMC1 TRANSMIT DATA
FIRST BIT OF
FIRST 5-BIT
TRANSMIT
CHARACTER
(LSB)
NOTES:
1. SMCLK is an internal clock derived from an external CLKPIN or a baud rate generator.
2. This example shows the SMC receiver and transmitter enabled separately. If the REN
and TEN bits were set at the same time, a single falling edge of SMSYN would
synchronize both.
FIVE 1's
ASSUME
CHARACTER
LENGTH
EQUALS 5
TRANSMISSION
COULD BEGIN
HERE IF TX FIFO
NOT LOADED IN
TIME
FIVE 1's ARE SENT
F
re
e
sc
a
le
S
e
m
ic
o
n
d
u
c
to
r,
I
Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
n
c
..
.