
Serial Communications Interface (SCI)
SCI Registers
MC68HC11E Family
—
Rev. 4
Technical Data
MOTOROLA
Serial Communications Interface (SCI)
159
RCKB
—
SCI Baud Rate Clock Check Bit (Test)
SCR[2:0]
—
SCI Baud Rate Select Bits
Selects receiver and transmitter bit rate based on output from baud
rate prescaler stage. Refer to
Figure 7-8
and
Figure 7-9
.
The prescaler bits, SCP[2:0], determine the highest baud rate, and
the SCR[2:0] bits select an additional binary submultiple (
÷
1,
÷
2,
÷
4,
through
÷
128) of this highest baud rate. The result of these two
dividers in series is the 16X receiver baud rate clock. The SCR[2:0]
bits are not affected by reset and can be changed at any time,
although they should not be changed when any SCI transfer is in
progress.
Figure 7-8
and
Figure 7-9
illustrate the SCI baud rate timing chain.
The prescaler select bits determine the highest baud rate. The rate
select bits determine additional divide by two stages to arrive at the
receiver timing (RT) clock rate. The baud rate clock is the result of
dividing the RT clock by 16.