SERIAL I/O
11.2 Block description
Transmit data is set into the UARTi transmit buffer register. Set the transmit data into the low-order byte
of this register when the microcomputer operates in the clock synchronous serial I/O mode or when a 7-
bit or 8-bit length of transfer data is selected in the UART mode. When a 9-bit length of transfer data is
selected in the UART mode, set the transmit data into the UARTi transmit buffer register as follows:
•Bit 8 of the transmit data into bit 0 of high-order byte of this register.
•Bits 7 to 0 of the transmit data into the low-order byte of this register.
The transmit data which has been set in the UARTi transmit buffer register is transferred to the UARTi
transmit register when the transmission conditions are satisfied, and then it is output from the TxDi pin
synchronously with the transfer clock. The UARTi transmit buffer register becomes empty when the data
set in the UARTi transmit buffer register has been transferred to the UARTi transmit register. Accordingly,
the user can set the next transmit data.
When the “MSB first” is selected in the clock synchronous serial I/O mode, bit position of set data is
reversed, and then the data of which bit position was reversed will be written, as a transmit data, into the
UARTi transmit buffer register. (Refer to section “11.3.2 Transfer data format.”) Transmit operation itself
is the same whichever format is selected, “LSB first” or “MSB first.”
When quitting the transmission which is in progress and setting the UARTi transmit buffer register again,
follow the procedure described bellow:
ꢀ Clear the serial I/O mode select bits (bits 2 to 0 at addresses 3016, 3816 and B016) to “000 ” (serial I/O
2
disabled).
ꢀ Set the serial I/O mode select bits again.
ꢀ Set the transmit enable bit (bit 0 at addresses 3516, 3D16 and B516) to “1” (transmission enabled) and set
transmit data in the UARTi transmit buffer register.
7905 Group User’s Manual Rev.1.0
11-11
RENESAS [ RENESAS TECHNOLOGY CORP ]
