INTERNAL SPECIFICATIONS
103
Table 4-16 Serial port operation modes
SM0
0
0
1
1
SM1
0
1
0
1
Mode
0
1
2
3
Function
I/O extension
10-bit frame UART
11-bit frame UART
11-bit frame UART
Baud rate
1/12 F
OSC
Vareable
1/32 F
OSC
or 1/64 F
OSC
Vareable
Note: F
OSC
denotes frequency of fundamental oscillator (XTAL1·2).
4.6.2.2 SBUF (serial port buffer register)
SBUF is an 8-bit special function register used to store transmitting and receiving data.
Although the SBUF is specified by the same data address 99H for both writing and reading,
physically separate registers are specified. That is, the sending circuit SBUF is specified by
instructions where SBUF is used as a destination operand, and the receiving circuit SBUF
is specified by instructions where SBUF is used as a source operand.
4.6.2.3 TCLK
TCLK controls selection of the baud rate clock source for the transmitting circuit when in mode
1 or 3.
The timer/counter 2 overflow becomes the transmitting circuit baud rate clock source when
TCLK is set in mode 1 or 3. And the timer/counter 1 overflow becomes the transmitting circuit
baud rate clock source if TCLK is cleared.
TCLK has no effect on the baud rate clock source when in mode 0 or 2. TCLK is located at
bit 4 of T2CON (timer/counter 2 control register) specified by data address 0C8H. This bit can
also be specified by bit address 0CCH.
4.6.2.4 RCLK
RCLK controls selection of the baud rate clock source for the receiving circuit when in mode
1 or 3.
The timer/counter 2 overflow becomes the receiving circuit baud rate clock source when
RCLK is set in mode 1 or 3. And the timer/counter 1 overflow becomes the receiving circuit
baud rate clock source if RCLK is cleared.
RCLK has no effect on the baud rate clock source when in mode 0 or 2. RCLK is located at
bit 5 of T2CON (timer/counter 2 control register) specified by data address 0C8H. This bit can
also be specified by bit address 0CDH.
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