M68HC11
REFERENCE MANUAL
ASYNCHRONOUS SERIAL COMMUNICATIONS INTERFACE
MOTOROLA
9-9
9.2.3 SCI Control Register 1 (SCCR1)
The SCCR1 contains control bits relate to the 9-bit data character format and the re-
ceiver wake-up feature. Four of the bits in this register are not used and always read
as zeros.
R8 — Receive Data Bit 8
When the SCI system is configured for 9-bit data characters, this bit acts as an extra
(ninth) bit of the RDR. The MSB of received characters is transferred into this bit at the
same time the remaining eight bits are transferred from the serial receive shifter to the
SCDR.
T8 — Transmit Data Bit 8
When the SCI system is configured for 9-bit data characters, this bit acts as the extra
(ninth) bit of the TDR. When the low-order eight bits of a transmit character are trans-
ferred from the SCDR to the serial transmit shift register, this bit is transferred to the
ninth bit position of the shifter. In cases where the sense of this bit is the same as it
was for the previous character, it is not necessary to write to this bit before transmis-
sion of the new character. For example, if the 9-bit format is used to get an extra stop
bit (logic one), the T8 bit is written to one before transmitting the first character, and no
other writes are needed.
M — SCI Character Length
0 = One start bit, eight data bits, one stop bit
1 = One start bit, nine data bits, one stop bit
The M bit controls the character length for both the transmitter and receiver at the
same time. The 9-bit data format is most commonly used for an extra stop bit or in con-
junction with the address-mark wake-up method, but it can also be used for parity.
Table 9-2 Baud-Rate Selects
SCR
2
SCR
1
SCR
0
Divi-
sion
Factor
Highest Baud Rate (from
Table 9-1
)
32.768K
Baud
SCI Baud Rate
131.072K Baud 32.768K Baud 76.80K Baud 19.20K Baud 9600 Baud
65.536K Baud
16.384K Baud 38.40K Baud
32.768K Baud
8192 Baud
19.20K Baud
16.384K Baud
4096 Baud
9600 Baud
8192 Baud
2048 Baud
4800 Baud
4096 Baud
1024 Baud
2400 Baud
2048 Baud
512 Baud
1200 Baud
1024 Baud
256 Baud
600 Baud
131.072K
Baud
76.80K
Baud
19.20K
Baud
9600
Baud
0
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
1
2
4
8
9600 Baud
4800 Baud
2400 Baud
1200 Baud
600 Baud
300 Baud
150 Baud
4800 Baud
2400 Baud
1200 Baud
600 Baud
300 Baud
150 Baud
75 Baud
16
32
64
128
SCCR1 —
SCI Control Register 1
$102C
BIT 7
R8
U
6
5
0
0
4
M
0
3
2
0
0
1
0
0
BIT 0
0
0
T8
U
WAKE
0
RESET: