mpc89x54a Megawin Technology, mpc89x54a Datasheet - Page 20

• Manufacturer Part Number: mpc89x54a
• Description: 8-bit Micro-controller
• Manufacturer: Megawin Technology

Baud-Rate Generator Mode (BRG)
Timer2 can be configured to generate various baud-rate. 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:
20
OSC/12
T2 pin
T2EX pin
C//T2
Baud Rate =
Baud Rate =
TR2
0
1
[32 x [65536 – (RCAP2H, RCAP2L) ] ]
Timer2 overflow rate
EXEN2
0
1
Oscillator Frequency
16
MPC89x54A Data Sheet
EXF2
RCAP2L[7:0]
TL2[7:0]
Timer2 interrupt
RCAP2H[7:0]
TH2[7:0]
(counting T2EX)
“1”
“1”
(as a timer)
Timer1 overflow
“0”
“0”
2
“0” “1”
TCLK
RCLK
MEGAWIN
16
TX Clock
SMOD
16
RX Clock