TDA8029HLSLASHC2 datasheet(16/58 Pages) PHILIPS

16 / 58 page

2003 Oct 30

Philips Semiconductors

Product speciﬁcation

Low power single card reader

TDA8029

8.2.4

BAUD RATE GENERATOR MODE

Bits TCLK and/or RCLK in register T2CON allow the serial

port transmit and receive baud rates to be derived from

either timer 1 or 2. When TCLK = 0, timer 1 is used as the

serial port transmit baud rate generator. When TCLK = 1,

timer 2 is used. 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.

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 the

overflow rate of timer 2, given by equation (1):

(1)

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. 1/12 fosc). As a baud rate generator, it increments every

state time (i.e. 1/2fosc). Thus the modes 1 and 3 baud rate

formula is as Equation (2):

(2)

Where (RCAP2H, RCAP2L) is the contents of RCAP2H

and RCAP2L registers taken as a 16-bit unsigned integer.

The timer 2 as a baud rate generator is valid only if

RCLK = 1 and/or TCLK = 1 in the 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 HIGH to LOW transition on T2EX

(Timer/counter 2 trigger input) will set the EXF2 (T2

external) flag but will not cause a reload from (RCAP2H

and RCAP2L) to (TH2 and TL2). Therefore, when timer 2

is used 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, never try

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

timer 2 is incremented every state time (1/2fosc) or

asynchronously from controller I/O 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. See Fig.5 for an overview.

Baud rate

Timer 2 overflow rate

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

Baud rate

Oscillator frequency

65536

RCAP2H, RCAP2L

()

–

[]

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

Table 9

Timer 2 generated commonly used baud rates

BAUD RATE

CRYSTAL OSCILLATOR

FREQUENCY

TIMER

RCAP2H (HEX)

RCAP2L (HEX)

375k

12 MHz

9.6k

12 MHz

2.8k

12 MHz

2.4k

12 MHz

1.2k

12 MHz

300

12 MHz

110

12 MHz

300

6 MHz

110

6 MHz

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