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
16
Baud Rate =
(counting T2EX)
Baud Rate =
Oscillator Frequency
[32 x [65536 – (RCAP2H, RCAP2L) ] ]
(as a timer)
Timer1 overflow
2
“0” “1”
SMOD
OSC/12
T2 pin
C//T2
TR2
“1”
RCAP2L[7:0]
RCAP2H[7:0]
0
1
0
1
TL2[7:0]
TH2[7:0]
“1”
“0”
RCLK
16
“0”
TCLK
16
TX Clock
RX Clock
T2EX pin
EXF2
Timer2 interrupt
EXEN2
MEGAWIN
MPC89x52A Data Sheet
19
MEGAWIN [ MEGAWIN TECHNOLOGY CO., LTD ]
