
Serial Communications Interface (SCI)
SCI Registers
MC68HC11E Family
—
Rev. 4
Technical Data
MOTOROLA
Serial Communications Interface (SCI)
157
FE
—
Framing Error Flag
FE is set when a 0 is detected where a stop bit was expected. Clear
the FE flag by reading SCSR with FE set and then reading SCDR.
0 = Stop bit detected
1 = Zero detected
Bit 0
—
Unimplemented
Always reads 0
7.8.5 Baud Rate Register
Use this register to select different baud rates for the SCI system. The
SCP[1:0] (SCP[2:0] in MC68HC(7)11E20) bits function as a prescaler for
the SCR[2:0] bits. Together, these five bits provide multiple baud rate
combinations for a given crystal frequency. Normally, this register is
written once during initialization. The prescaler is set to its fastest rate by
default out of reset and can be changed at any time. Refer to
Table 7-1
for normal baud rate selections.
TCLR
—
Clear Baud Rate Counter Bit (Test)
SCP[2:0]
—
SCI Baud Rate Prescaler Select Bits
NOTE:
SCP2 applies to MC68HC(7)11E20 only. When SCP2 = 1, SCP[1:0]
must equal 0s. Any other values for SCP[1:0] are not decoded in the
prescaler and the results are unpredictable. Refer to
Figure 7-8
and
Figure 7-9
.
Address:
$102B
Bit 7
6
5
4
3
2
1
Bit 0
Read:
TCLR
SCP2
SCP1
SCP0
RCKB
SCR2
SCR1
SCR0
Write:
Reset:
0
0
0
0
0
U
U
U
U = Unaffected
Figure 7-7. Baud Rate Register (BAUD)