MC68HC11F1 Datasheet, PDF (44/68 Pages) Motorola, Inc – Technical Summary 8-Bit Microcontroller

9.2 SCI Registers
BAUD — Baud Rate
RESET:
Bit 7
TCLR
0
6
SCP2
0
5
SCP1
0
4
SCP0
0
3
RCKB
0
2
SCR2
U
1
SCR1
U
Bit 0
SCR0
U
$x02B
TCLR — Clear Baud Rate Counters (TEST)
Bit 6 — Not implemented. Reads always return zero and writes have no effect.
RCKB — SCI Baud-Rate Clock Check (TEST)
SCP[2:0] — SCI Baud Rate Prescaler Selects
These bits determine the baud rate prescaler frequency. Refer to Table 21 and Figure 11.
SCR[2:0] — SCI Baud Rate Selects
These bits determine the receiver and transmitter baud rate. Refer to Table 22 and Figure 11.
Table 21 Baud Rate Prescaler Selection
SCP[2:0]
X00
001
X10
X11
101
Divide
Internal
Clock By
1
3
4
13
9
XTAL =
4.0 MHz
62500
20833
15625
4800
—
XTAL =
4.9152 MHz
76800
25600
19200
5908
—
Prescaler Output¹
XTAL = XTAL = XTAL = XTAL = XTAL = XTAL =
8.0 MHz 10.0 MHz 12.0 MHz 16.0 MHz 20.0 MHz 24.0 MHz
125000 156250 187500 250000 312500 375000
41667 52083 62500 83333 104167 125000
31250 38400 46875 62500 76800 93750
9600 12019 14423 19200 24038 28846
—
—
20830
—
—
—
NOTES:
1. A blank table cell indicates that an uncommon rate results.
SCR[2:0]
000
001
010
011
100
101
110
111
Table 22 Baud Rate Selection
Divide
Prescaler By
1
2
4
8
16
32
64
128
Prescaler
Output =
4800
4800
2400
1200
600
300
150
75
—
Prescaler
Output =
9600
9600
4800
2400
1200
600
300
150
75
Baud Rate
Prescaler
Output =
19200
19200
9600
4800
2400
1200
600
300
150
Prescaler
Output =
38400
38400
19200
9600
4800
2400
1200
600
300
Prescaler
Output =
76800
76800
38400
19200
9600
4800
2400
1200
600
The prescaler bits SCP[2:0] determine the highest baud rate, and the SCR[2:0] bits select an additional
binary submultiple (divide by 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. They should not be changed, however, when an SCI transfer is in progress.
MOTOROLA
44
MC68HC11F1/FC0
MC68HC11FTS/D