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7751 Group User’s Manual
7–45
SE R IAL I/ O
7.4 Clock asynchronous serial I/O (UART) mode
Fig. 7.4.6 Example of transmit timing when transfer data length is 8 bits (when parity enabled,
selecting 1 stop bit)
Fig. 7.4.7 Example of transmit timing when transfer data length is 9 bits (when parity disabled,
selecting 2 stop bits)
Tc
D
0
D
1
D
2
D
3
D
4
D
5
D
6
D
7
ST
P
SP
D
0
D
1
D
0
D
1
D
2
D
3
D
4
D
5
D
6
D
7
ST
P
SP
ST
T
ENDi
TxD
i
CTS
i
“0”
“1”
“0”
“1”
“L”
“H”
“0”
“1”
“0”
“1”
T
ENDi
: Next transmit conditions are examined when this signal level is “H.”
(T
ENDi
is an internal signal. Accordingly, it cannot be read from an external.)
Tc: 16(n + 1)/fi or 16(n + 1)/f
fi: BRGi count source frequency (f
2
/f
4
, f
16
/f
32
, f
64
/f
128
, f
512
/f
1024
)
f
: BRGi count source frequency (external clock)
n: Value set to BRGi
Transfer clock
Transmit enable bit
Transmit buffer
empty flag
Transmit register
empty flag
UARTi transmit
interrupt request bit
Data is set in UARTi transmit buffer register.
Start bit
Parity bit
Cleared to “0” when interrupt request is accepted or cleared by software.
The above timing diagram applies to
the following conditions:
G
Parity enabled
G
1 stop bit
G
CTS function selected
UARTi transmit register
UARTi transmit buffer register
Stopped because transmit enable bit = “0”
Stop bit
D
0
D
1
D
2
D
3
D
4
D
5
D
6
D
7
ST
D
8
D
0
D
1
D
2
D
3
D
4
D
5
D
6
D
7
ST
SP
D
0
D
1
ST
D
8
SP
SPSP
“0”
“1”
“0”
“1”
“0”
“1”
Tc
“0”
“1”
T
ENDi
TxD
i
T
ENDi
: Next transmit conditions are examined when this signal level is “H.”
(T
ENDi
is an internal signal. Accordingly, it cannot be read from an external.)
Tc: 16(n + 1)/fi or 16(n + 1)/f
fi: BRGi count source frequency (f
2
/f
4
, f
16
/f
32
, f
64
/f
128
, f
512
/f
1024
)
f
: BRGi count source frequency (external clock)
n: Value set to BRGi
Transfer clock
Transmit enable bit
Transmit buffer
empty flag
Transmit register
empty flag
UARTi transmit
interrupt request bit
Data is set in UARTi transmit buffer register.
Start bit
Cleared to “0” when interrupt request is accepted or cleared by software.
The above timing diagram applies to
the following conditions:
G
Parity disabled
G
2 stop bits
G
CTS function disabled
UARTi transmit register
UARTi transmit buffer register
Stopped because transmit enable bit = “0”
Stop bit
Stop bit