APPLICATION
2.5 Serial I/O
3822 GROUP USER’S MANUAL
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sBRG count source selection bit (bit 0)
Selects a count source to be input to the BRG. In the “0” state, an undivided XIN input signal is input
to the BRG. In the “1” state, an XIN input signal divided by 4 is input to the BRG.
sSerial I/O synchronization clock selection bit (bit 1)
Selects a synchronizing clock to be used in the serial I/O.
qClock synchronous mode
When this bit is set to “0,” a BRG output divided by 4 becomes a shift clock.
In the “1” state, an external clock (P46/SCLK pin input) becomes a shift clock as it is.
qUART mode
In the “0” state, a BRG output divided by 16 becomes a shift clock. In the “1” state, an external clock
(P46/SCLK pin input) divided by 16 becomes a shift clock.
sSRDY output enable bit (bit 2)
When the SRDY function is used in the clock synchronous mode, set this bit to “1.” In the “0” state,
the P47/SRDY pin functions as an I/O port P47.
In the UART mode, the value of this bit is invalid, so that the P47/SRDY pin functions as an I/O port
P47.
sTransmit interrupt source selection bit (bit 3)
Determines a source which generates a serial I/O transmit interrupt request. In the “0” state, a serial
I/O transmit interrupt request occurs at the time when the values of the transmit buffer register are
transferred to the transmit shift register.
In the “1” state, a serial I/O transmit interrupt request occurs at the time when the shift operation of
the transmit shift register is completed.
sTransmit enable bit (bit 4)
Controls a transmit operation. This bit controls as shown in Table 2.5.3 only when the serial I/O enable
bit is “1” (serial I/O enabled). When the serial I/O enable bit is “0” (serial I/O disabled), this bit is
invalid.
Transmit buffer empty flag V1
Transmit enable bit
Table 2.5.3 Control contents of transmit enable bit
Flag function is valid
Transmit shift register
shift completion flagV2
P45/TXD pin function
0
Port P45
Set to “0”
Data transmit pin TXD
1
V1: Bit 0 of serial I/O status register
V2: Bit 2 of serial I/O status register