Baud-Rate Generator Mode (BRG)
Timer2 can be configured to generate various baud-rates. Bit TCLK and/or RCLK in
T2CON allow the serial port transmit and receive baud rates to be derived from either
Timer1 or Timer2. When TCLK=0, Timer1 is used as the serial port transmit baud rate
generator. When TCLK=1, Timer2 is used as the serial port transmit baud rate generator.
RCLK has the same effect for the serial port baud rate. With these two bits, the serial port
can have different receive and transmit baud rates – one generated from Timer1 and the
other from Timer2.
In BRG mode, Timers is operated very like auto-reload up-only mode except that the
T2EX pin cannot control reload. An overflow on Timer2 will load RCAP2H, RCAP2L
contents onto Timer2, but TF2 will not be set. A 1-to-0 transition on P2EX pin can set
EXF2 to request interrupt service if EXEN2=1.
The baud rate in UART Mode1 and Mode3 are determined by Timer2’s overflow rate
given below:
Timer2 overflow rate
(counting T2EX)
Baud Rate =
16
Oscillator Frequency
(as a timer)
Baud Rate =
[32 x [65536 – (RCAP2H, RCAP2L) ] ]
Timer1 overflow
2
“0”
“1”
SMOD
0
“1”
“1”
“0”
0
1
TL2[7:0]
TH2[7:0]
OSC/12
T2 pin
RCLK
1
16
C//T2
TR2
“0”
TCLK
RX Clock
TX Clock
RCAP2L[7:0]
RCAP2H[7:0]
16
EXF2
Timer2 interrupt
T2EX pin
EXEN2
MEGAWIN
MPC89x515A Data Sheet
19
MEGAWIN [ MEGAWIN TECHNOLOGY CO., LTD ]
