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CHAPTER 20 SERIAL INTERFACE CHANNEL 2
(2) Communication operation
(a) Data format
The transmit/receive data format is shown in Figure 20-7.
Figure 20-7. Asynchronous Serial Interface Transmit/Receive Data Format
One data frame consists of the following bits.
• Start bit ................... 1 bit
• Character bits ......... 7 bits/8 bits
• Parity bit.................. Even parity/odd parity/0 parity/no parity
• Stop bit(s) ............... 1 bit/2 bits
The specification of character bit length, parity selection, and specification of stop bit length for each
data frame is carried out with asynchronous serial interface mode register (ASIM).
When 7 bits are selected as the number of character bits, only the lower 7 bits (bits 0 to 6) are valid;
in transmission the most significant bit (bit 7) is ignored, and in reception the most significant bit (bit
7) is always “0”.
The serial transfer rate is selected by ASIM and the baud rate generator control register (BRGC).
If a serial data receive error is generated, the receive error contents can be determined by reading the
status of the asynchronous serial interface status register (ASIS).
D0 D1 D2 D3 D4 D5 D6 D7
Parity
Bit
Stop Bit
Start
Bit
One Data Frame
Character Bit