SyncMOS Technologies International, Inc.
SM89T16R1
8-Bits Micro-controller
With 64KB Flash ROM & 1KB RAM & Two UART & RTC & ADC & PWM embedded
Serial Port Mode 1:
Timer 1
Timer 2 Overflow
STOP
Overflow
Internal
PARIN
RxD
1/2
Data Bus
SOUT
P3.0 Alternate
Input function
Write to
SBUF
START
LOAD
SMOD=
0
1
(SMOD 1)
CLOCK
TCLK
1
1
Transmit Shift Register
TX START
TX CLOCK
TX SHIFT
1/16
1/16
TI
RI
Serial Port Interrupt
TxD
RCLK
0
SHIFT CLOCK
LOAD SBUF
RX SHIFT
P3.1 Alternate
Input function
SAMPLE
RX CLOCK
1- To-0
READ SBUF
SBUF
Detector
RX START
CLOCK
Internal
SBUF
RB8
PAROUT
Data Bus
Bit
RxD
D8
Detector
SIN
P3.0 Alternate
Input function
Receive Shift Register
Mode 2
This mode uses a total of 11 bits in asynchronous full-duplex communication. The functional description is shown in
the figure below. The frame consists of one start bit (0), 8 data bits (LSB first), a programmable 9th bit (TB8) and a
stop bit (0). The 9th bit received is put into RB8. The baud rate is programmable to 1/32 or 1/64 of the oscillator
frequency, which is determined by the SMOD bit in PCON SFR. Transmission begins with a write to SBUF. The
serial data is brought out on to TxD pin following the first rollover of the divide by 16 counter. Thus the transmission
is synchronized to the divide by 16 counter, and not directly to the write to SBUF signal. After all 9 bits of data are
transmitted the stop bit is transmitted. The TI flag is set after the stop bit has been put out on TxD pin. This will be at
the 11th rollover of the divide by 16 counter after a write to SBUF. Reception is enabled only if REN is high. The
serial port actually starts the receiving of serial data, with the detection of a falling edge on the RxD pin. The 1-to-0
detector continuously monitors the RxD line, sampling it at the rate of 16 times the selected baud rate. When a falling
edge is detected, the divide by 16 counter is immediately reset. This helps to align the bit boundaries with the
rollovers of the divide by 16 counter. The 16 states of the counter effectively divide the bit time into 16 slices. The bit
detection is done on a best of three bases. The bit detector samples the RxD pin, at the 8th, 9th and 10th counter states.
By using a majority 2 of 3 voting system, the bit value is selected. This is done to improve the noise rejection feature
of the serial port.
If the first bit detected after the falling edge of RxD pin, is not 0, then this indicates an invalid start bit, and the
reception is immediately aborted. The serial port again looks for a falling edge in the RxD line. If a valid start bit is
detected, then the rest of the bits are also detected and shifted into the SBUF. After shifting in 9 data bits, there is one
more shift to do, after which the SBUF and RB8 are loaded and RI is set. However certain conditions must be met
before the loading and setting of RI can be done.
RI must be 0 and Either SM2 = 0, or the received 9th bit = 1.
If these conditions are met, then the 9th bit goes to RB8, the 8 data bits go into SBUF and RI is set. Otherwise the
received frame may be lost. After the middle of the stop bit, the receiver goes back to looking for a 1-to-0 transition
on the RxD pin.
Specifications subject to change without notice contact your sales representatives for the most recent information.
Ver 2.1 SM89T16R1 08/2006
22
SYNCMOS [ SYNCMOS TECHNOLOGIES,INC ]
