AT89LP51RB2 datasheet(93/254 Pages) ATMEL

93 / 254 page

3722A–MICRO–10/11

AT89LP51RB2/RC2/IC2 Preliminary

Figure 14-5. Timer 2 Diagram: Auto-Reload Mode (DCEN = 1)

14.4

Baud Rate Generator

Timer 2 is selected as the baud rate generator by setting TCLK and/or RCLK in T2CON (Table

14-3). 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 14-6.

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 UART Modes 1 and 3 are determined by Timer 2’s overflow rate according to

the following equation.

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 baud rate formulas are given below.

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 14-6. 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-

rupt. Note too, that if EXEN2 is set, a 1-to-0 transition in T2EX will set EXF2 but will not cause a

reload from (RCAP2H, RCAP2L) to (TH2, TL2). Thus when Timer 2 is in use as a baud rate gen-

erator, T2EX can be used as an extra external interrupt. Also note that the Baud Rate and

Frequency Generator modes may be used simultaneously.

÷TPS

CLKSYS

Modes 1 and 3 Baud Rates

Timer 2 Overflow Rate

------------------------------------------------------------

Modes 1, 3

Baud Rate

SYS

65536

RCAP2H,RCAP2L

()

–

[]

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AT89LP51RB2 Datasheet(PDF) 93 Page - ATMEL Corporation