P89C51RC2BASLASH01 datasheet(19/68 Pages) PHILIPS

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Philips Semiconductors

Preliminary data

P89C51RA2/RB2/RC2/RD2xx

80C51 8-bit Flash microcontroller family

8KB/16KB/32KB/64KB ISP/IAP Flash with 512B/512B/512B/1KB RAM

2002 Jul 18

C/T2 = 0

C/T2 = 1

TR2

Control

TL2

(8-bits)

TH2

(8-bits)

÷ 16

RCAP2L

RCAP2H

EXEN2

Control

EXF2

Timer 2

Interrupt

T2EX Pin

Transition

Detector

Reload

÷ 2

“0”

“1”

RX Clock

÷ 16

TX Clock

“0”

“1”

“0”

“1”

Timer 1

Overflow

Note availability of additional external interrupt.

SMOD

RCLK

TCLK

SU01629

n = 1 in 6-clock mode

n = 2 in 12-clock mode

OSC

÷ n

T2 Pin

Figure 11. Timer 2 in Baud Rate Generator Mode

Table 4.

Timer 2 Generated Commonly Used

Baud Rates

Baud Rate

Timer 2

12-clock

mode

6-clock

mode

Osc Freq

RCAP2H

RCAP2L

375 k

750 k

12 MHz

9.6 k

19.2 k

12 MHz

4.8 k

9.6 k

12 MHz

2.4 k

4.8 k

12 MHz

1.2 k

2.4 k

12 MHz

300

600

12 MHz

110

220

12 MHz

300

600

6 MHz

110

220

6 MHz

Baud Rate Generator Mode

Bits TCLK and/or RCLK in T2CON (Table 4) allow the serial port

transmit and receive baud rates to be derived from either Timer 1 or

Timer 2. When TCLK= 0, Timer 1 is used as the serial port transmit

baud rate generator. When TCLK= 1, Timer 2 is used as the serial

port transmit baud rate generator. RCLK has the same effect for the

serial port receive baud rate. With these two bits, the serial port can

have different receive and transmit baud rates – one generated by

Timer 1, the other by Timer 2.

Figure 11 shows the Timer 2 in baud rate generation mode. The baud

rate generation mode is like 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 given below:

Modes 1 and 3 Baud Rates

+ Timer 2 Overflow Rate

The timer can be configured for either “timer” or “counter” operation.

In many applications, it is configured for “timer” operation (C/T2=0).

Timer operation is different for Timer 2 when it is being used as a

baud rate generator.

Usually, as a timer it would increment every machine cycle (i.e.,

1/6 the oscillator frequency in 6-clock mode, 1/12 the oscillator

frequency in 12-clock mode). As a baud rate generator, it

increments at the oscillator frequency in 6-clock mode (OSC/2 in

12-clock mode). Thus the baud rate formula is as follows:

Oscillator Frequency

[n *

[65536

* (RCAP2H, RCAP2L)]]

Modes 1 and 3 Baud Rates =

* n =

16 in 6-clock mode

32 in 12-clock mode

Where:

(RCAP2H, RCAP2L)= The content of RCAP2H and

RCAP2L taken as a 16-bit unsigned integer.

The Timer 2 as a baud rate generator mode shown in Figure 11, is

valid only if RCLK and/or TCLK = 1 in T2CON register. Note that a

rollover in TH2 does not set TF2, and will not generate an interrupt.

Thus, the Timer 2 interrupt does not have to be disabled when

Timer 2 is in the baud rate generator mode. Also if the EXEN2

(T2 external enable flag) is set, a 1-to-0 transition in T2EX

(Timer/counter 2 trigger input) will set EXF2 (T2 external flag) but

will not cause a reload from (RCAP2H, RCAP2L) to (TH2,TL2).

Therefore when Timer 2 is in use as a baud rate generator, T2EX

can be used as an additional external interrupt, if needed.

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