Serial Communications Interface (SCI)
Data Sheet
M68HC11E Family — Rev. 5
126
Serial Communications Interface (SCI)
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MOTOROLA
NF — Noise Error Flag
NF is set if majority sample logic detects anything other than a unanimous
decision. Clear NF by reading SCSR with NF set and then reading SCDR.
0 = Unanimous decision
1 = Noise detected
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
7.7.5 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
.
RCKB — SCI Baud Rate Clock Check Bit (Test)
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)
F
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n
.