
APPLICATION
2.5 Serial I/O
3822 GROUP USER’S MANUAL
2–102
2.5 Serial I/O
2.5.1 Explanation of operations
As a serial I/O, it is possible to select either the clock synchronous serial I/O mode or the clock asynchro-
nous serial I/O (UART) mode. This section describes operations in both the clock synchronous mode and
the clock asynchronous (UART) mode. When serial I/O is actually used, refer to “2.5.4 Register setting
example.”
(1) Clock synchronous serial I/O mode
In the clock synchronous mode, 8 shift clocks generated in the clock control circuit are used as
synchronizing clocks for transfer. In synchronization with these shift clocks, the transmit operation on
the transmitter and the receive operation on the receiver are simultaneously executed.
The transmitter transmits each 1-bit data from the P45/TxD pin in synchronization with the falling of
the shift clocks.
The receiver receives each 1-bit data from the P44/RxD pin in synchronization with the rising of the
shift clocks.
Figure 2.5.1 shows an external connection example in the clock synchronous mode.
Fig. 2.5.1 External connection example in clock synchronous mode
1/(n+1)
BRG
XIN
1/4
8
SCLK
TxD
RxD
TxD
3822
Internal clock is selected
External clock is selected
Receive buffer register
Receive shift register
Transmit shift register
Transmit buffer register
Clock control circuit
8
3822
Receive shift register
Receive buffer register
Transmit buffer register
Transmit shift register
1/4
SCLK
Clock control circuit