AT89C51RC-24PC View Datasheet(PDF) - Atmel Corporation
Part Name
Description
MFG CO.
'AT89C51RC-24PC' PDF : 36 Pages View PDF
14. Baud Rate Generator
Timer 2 is selected as the baud rate generator by setting TCLK and/or RCLK in T2CON (Table
5-2). Note that the baud rates for transmit and receive can be different if Timer 2 is used for the
receiver or transmitter and Timer 1 is used for the other function. Setting RCLK and/or TCLK
puts Timer 2 into its baud rate generator mode, as shown in Figure 14-1.
The baud rate generator mode is similar to the auto-reload mode, in that a rollover in TH2
causes the Timer 2 registers to be reloaded with the 16-bit value in registers RCAP2H and
RCAP2L, which are preset by software.
The baud rates in Modes 1 and 3 are determined by Timer 2’s overflow rate according to the fol-
lowing equation.
Mdes 1 and 3 Baud Rates = T----i-m-----e----r---2-----O-----v---e----r--f-l--o---w------R----a---t--e--
16
Figure 14-1. Timer 2 in Baud Rate Generator Mode
TIMER 1 OVERFLOW
NOTE: OSC. FREQ. IS DIVIDED BY 2, NOT 12
OSC
÷2
C/T2 = 0
T2 PIN
T2EX PIN
C/T2 = 1
TRANSITION
DETECTOR
TH2
TL2
CONTROL
TR2
RCAP2H RCAP2L
CONTROL
EXEN2
EXF2
÷2
"0" "1"
SMOD1
"1" "0"
"1" "0"
TIMER 2
INTERRUPT
RCLK
÷ 16
Rx
CLOCK
TCLK
÷ 16
Tx
CLOCK
The Timer can be configured for either timer or counter operation. In most applications, it is con-
figured for timer operation (CP/T2 = 0). The timer operation is different for Timer 2 when it is
used as a baud rate generator. Normally, as a timer, it increments every machine cycle (at 1/12
the oscillator frequency). As a baud rate generator, however, it increments every state time (at
1/2 the oscillator frequency). The baud rate formula is given below.
M-----o----d---e----s----1-----a----n---d-----3-- = ----------------O-----s---c---i-l--l-a---t--o---r----F----r--e---q---u----e---n---c---y-----------------
Baud Rate
32 x [65536-RCAP2H,RCAP2L)]
where (RCAP2H, RCAP2L) is the content of RCAP2H and RCAP2L taken as a 16-bit unsigned
integer.
Timer 2 as a baud rate generator is shown in Figure 14-1. This figure is valid only if RCLK or
TCLK = 1 in T2CON. Note that a rollover in TH2 does not set TF2 and will not generate an inter-
16 AT89C51RC
1920C–MICRO–03/05
Share Link: 
