SM39R08A5
8-Bit Micro-controller
with 8KB Flash
& 256B RAM embedded
The Serial Interface can operate in the following 4 modes:
SM0
0
0
1
1
SM1
0
1
0
1
Mode
0
1
2
3
Description
Shift register
8-bit UART
9-bit UART
9-bit UART
Board Rate
Fosc/12
Variable
Fosc/32 or Fosc/64
Variable
Here Fosc is the crystal or oscillator frequency.
7.1. Mode 0
Pin RXD serves as input and output. TXD outputs the shift clock. 8 bits are transmitted with LSB first. The baud rate is
fixed at 1/12 of the crystal frequency. Reception is initialized in Mode 0 by setting the flags in SCON as follows: RI = 0 and
REN = 1. In other modes, a start bit when REN = 1 starts receiving serial data.
Fig. 7-1: Transmit mode 0
Fig. 7-2: Receive mode 0
7.2. Mode 1
Pin RXD serves as input, and TXD serves as serial output. No external shift clock is used, 10 bits are transmitted: a start
bit (always 0), 8 data bits (LSB first), and a stop bit (always 1). On receive, a start bit synchronizes the transmission, 8
data bits are available by reading SBUF, and stop bit sets the flag RB8 in the Special Function Register SCON. In mode 1
either internal baud rate generator or timer 1 can be use to specify baud rate.
Fig. 7-3: Transmit mode 1
Specifications subject to change without notice contact your sales representatives for the most recent information.
ISSFD-M067
Ver B SM39R08A5 04/22/2013
- 26 -
SYNCMOS [ SYNCMOS TECHNOLOGIES,INC ]
