Table 8-7. Data Formats in Asynchronous Mode
Notes: SMR: Serial mode register
START: Start bit
STOP: Stop bit
P: Parity bit
MPB: Multiprocessor bit
(2) Clock: In asynchronous mode it is possible to select either an internal clock created by the on-
chip baud rate generator, or an external clock input at the SCK pin. The clock selection depends on
the C/A bit in the serial mode register (SMR) and the CKE0 and CKE1 bits in the serial control
register (SCR). Refer to table 8-6.
If an external clock is input at the SCK pin, its frequency should be 16 times the desired bit rate.
If the internal clock provided by the on-chip baud rate generator is selected and the SCK pin is used
for clock output, the output clock frequency is equal to the bit rate, and the clock pulse rises at the
center of the transmit data bits. Figure 8-3 shows the phase relationship between the output clock
and transmit data.
CHR
0
0
0
0
1
1
1
1
0
0
1
1
PE
0
0
1
1
0
0
1
1
—
—
—
—
MP
0
0
0
0
0
0
0
0
1
1
1
1
STOP
0
1
0
1
0
1
0
1
0
1
0
1
SMR Bits
1
2
3
4
5
6
7
8
9
10
11
12
S
S
S
S
S
S
S
S
S
S
S
S
8-Bit data
STOP
8-Bit data
STOP
STOP
8-Bit data
P
STOP
8-Bit data
P
STOP
STOP
7-Bit data
STOP
7-Bit data
STOP
STOP
7-Bit data
P
STOP
7-Bit data
P
STOP
STOP
8-Bit data
MPB
STOP
8-Bit data
MPB
STOP
STOP
7-Bit data
MPB
STOP
7-Bit data
MPB
STOP
STOP
185
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