
7470/7471/7477/7478 GROUP USER’S MANUAL
1-136
HARDWARE
1.13 Serial I/O
Each bit of the Serial I/O control register is described below.
2 BRG count source selection bit (CSS, bit 0)
This bit selects a count source to be input to the BRG.
“0”: f(XIN)/4
“1”: f(XIN)/16
2 Serial I/O synchronous clock selection bit (SCS, bit 1)
This bit selects a synchronous clock to be used for the serial I/O.
q In the clock synchronous serial I/O
“0”: The BRG output divided by 4 becomes a shift clock.
“1”: The external clock (P16/SCLK pin input) becomes a synchronous clock.
q In the UART
“0”: The BRG output divided by 16 becomes a shift clock.
“1”: The external clock (P16/SCLK pin input) divided by 16 becomes a synchronous clock.
2 SRDY output enable bit (SRDY, bit 2)
This bit selects whether the P17/SRDY pin is used as P17 or as serial I/O pin SRDY or SRDY output
disable.
q In the clock synchronous serial I/O
“0”: SRDY pin output disable (used as port P17)
“1”: SRDY pin output enable (used as serial I/O pin SRDY)
q In the UART
The P17/SRDY pin is used as P17 regardless of the value of this bit.
2 Transmit interrupt request selection bit (TIC, bit 3)
This bit determines a source for generating a transmit interrupt request.
“0”: When the contents of the Transmit buffer register are transferred to the Transmit shift
register, a transmit interrupt request is generated.
“1”: When the shift operation of the Transmit shift register terminates, a transmit interrupt
request is generated.
2 Transmit enable bit (TE, bit 4)
This bit controls a transmit operation.
q When the serial I/O enable bit (bit 7) is “0” (serial I/O disable)
The transmit enable bit is invalid.
q When the serial I/O enable bit (bit 7) is “1” (serial I/O disable)
The control shown in Table 1.13B.9 is exerted.
1: Bit 0 of Serial I/O status register
2: Bit 2 of Serial I/O status register
Transmit enable bit
0
1
Transmit buffer
empty flag1
Cleared to “0”
Flag function is valid.
Transmit shift
completion flag2
Cleared to “0”
Flag function is valid.
P15/TXD pin function
Port P15
Serial I/O data transmit pin TXD
Table 1.13B.9 Transmit enable bit function