P80C32 datasheet(21/62 Pages) PHILIPS

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Philips Semiconductors

Product data

P80C3xX2; P80C5xX2;

P87C5xX2

80C51 8-bit microcontroller family

4K/8K/16K/32K ROM/OTP, low voltage (2.7 to 5.5 V),

low power, high speed (30/33 MHz)

2003 Jan 24

OSC

÷ n

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

T2 Pin

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

SU01625

n = 1 in 6-clock mode

n = 2 in 12-clock mode.

Figure 11. Timer 2 in Baud Rate Generator Mode

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 or 1/12 the oscillator

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

increments at the oscillator frequency in 6-clock mode or at 1/2 the

oscillator frequency in 12-clock mode. Thus the baud rate formula is

as follows:

Oscillator Frequency

[65536

* (RCAP2H, RCAP2L)]]

Modes 1 and 3 Baud Rates =

Where:

n = 16 in 6-clock mode, 32 in 12-clock mode.

(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.

When Timer 2 is in the baud rate generator mode, one should not try

to read or write TH2 and TL2. As a baud rate generator, Timer 2 is

incremented every state time (osc/2) or asynchronously from pin T2;

under these conditions, a read or write of TH2 or TL2 may not be

accurate. The RCAP2 registers may be read, but should not be

written to, because a write might overlap a reload and cause write

and/or reload errors. The timer should be turned off (clear TR2)

before accessing the Timer 2 or RCAP2 registers.

Table 5 shows commonly used baud rates and how they can be

obtained from Timer 2.

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