SM39R08A5
8-Bit Micro-controller
with 8KB Flash
& 256B RAM embedded
Fig. 7-4: Receive mode 1
7.3. Mode 2
This mode is similar to Mode 1, with two differences. The baud rate is fixed at 1/32 (SMOD=1) or 1/64(SMOD=0) of
oscillator frequency and 11 bits are transmitted or received: a start bit (0), 8 data bits (LSB first), a programmable 9
th
bit,
and a stop bit (1). The 9
th
bit can be used to control the parity of the serial interface: at transmission, bit TB8 in SCON is
output as the 9
th
bit, and at receive, the 9
th
bit affects RB8 in Special Function Register SCON.
7.4. Mode 3
The only difference between Mode 2 and Mode 3 is that in Mode 3 either internal baud rate generator or timer 1 can be
use to specify baud rate.
Fig. 7-5: Transmit modes 2 and 3
Fig. 7-6: Receive modes 2 and 3
7.5. Multiprocessor communication
The feature of receiving 9 bits in Modes 2 and 3 of Serial Interface can be used for multiprocessor communication. In this
case, the slave processors have bit SM2 in SCON. When the master processor outputs slave’s address, it sets the 9
th
bit
to 1, causing a serial port receive interrupt in all the slaves. The slave processors compare the received byte with their
network address. If there is a match, the addressed slave will clear SM2 and receive the rest of the message, while other
slaves will leave SM2 bit unaffected and ignore this message. After addressing the slave, the host will output the rest of
the message with the 9
th
bit set to 0, so no serial port receive interrupt will be generated in unselected slaves.
Specifications subject to change without notice contact your sales representatives for the most recent information.
ISSFD-M067
Ver B SM39R08A5 04/22/2013
- 27 -
SYNCMOS [ SYNCMOS TECHNOLOGIES,INC ]
