APPLICATION
2.5 Serial I/O1
3820 GROUP USER’S MANUAL
2–125
I
BRG count source selection bit (bit 0)
This bit selects a count source to be input to the BRG. In the “0” state, an undivided X
IN
input signal
is input to the BRG. In the “1” state, an X
IN
input signal divided by 4 is input to the BRG.
I
Serial I/O1 synchronization clock selection bit (bit 1)
This bit selects a synchronizing clock to be used in the serial I/O1.
G
Clock 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 (P4
6
/S
CLK1
pin input) becomes a shift clock as it is.
G
UART mode
In the “0” state, a BRG output divided by 16 becomes a shift clock. In the “1” state, an external clock
(P4
6
/S
CLK1
pin input) divided by 16 becomes a shift clock.
I
S
RDY1
output enable bit (bit 2)
When the S
RDY1
function is used in the clock synchronous mode, set this bit to “1.” In the “0” state,
the P4
7
/S
RDY1
pin functions as an I/O port P4
7
.
In the UART mode, the value of this bit is invalid, so that the P4
7
/S
RDY1
pin functions as an I/O port
P4
7.
I
Transmit interrupt source selection bit (bit 3)
This bit determines a source which generates a serial I/O1 transmit interrupt request. In the “0” state,
a serial I/O1 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/O1 transmit interrupt request occurs at the time when the shift operation of
the transmit shift register is completed.
I
Transmit enable bit (bit 4)
This bit controls a transmit operation. This bit controls as shown in Table 2.5.3 only when the serial
I/O1 enable bit is “1” (serial I/O1 enabled). When the serial I/O1 enable bit is “0” (serial I/O1 disabled),
this bit is invalid.
Transmit buffer empty flag
8
1
Transmit enable bit
Table 2.5.3 Control contents of transmit enable bit
Flag function is valid
Transmit shift register
shift completion flag
8
2
P4
5
/T
X
D pin function
0
Port P4
5
Set to “0”
Data transmit pin T
X
D
1
8
1: Bit 0 of serial I/O1 status register
8
2: Bit 2 of serial I/O1 status register