TDA8029 Philips Semiconductors, TDA8029 Datasheet - Page 16

• Manufacturer Part Number: TDA8029
• Description: Low power single card reader
• Manufacturer: Philips Semiconductors

Philips Semiconductors
8.2.4
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):
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.
state time (i.e.
formula is as Equation (2):
Table 9 Timer 2 generated commonly used baud rates
2003 Oct 30
375k
9.6k
2.8k
2.4k
1.2k
300
110
300
110
Baud rate
Low power single card reader
1
/
12
f
BAUD RATE
osc
B
Baud rate
AUD RATE GENERATOR MODE
). As a baud rate generator, it increments every
=
1
/
----------------------------------------------------------------------------------------------- -
32
2
f
osc
). Thus the modes 1 and 3 baud rate
=
65536
Timer 2 overflow rate
------------------------------------------------------- -
Oscillator frequency
–
12 MHz
12 MHz
12 MHz
12 MHz
12 MHz
12 MHz
12 MHz
6 MHz
6 MHz
RCAP2H, RCAP2L
CRYSTAL OSCILLATOR
16
FREQUENCY
(1)
(2)
16
FF
FF
FF
FF
FE
FB
F2
FD
F9
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 (
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.
RCAP2H (HEX)
TIMER
FF
D9
B2
64
C8
1E
AF
8F
57
RCAP2L (HEX)
Product specification
1
TDA8029
/
2
f
osc
) or