AT89S52 Atmel Corporation, AT89S52 Datasheet - Page 15
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AT89S52
Manufacturer Part Number
AT89S52
Description
Manufacturer
Atmel Corporation
Datasheet
1.AT89S52.pdf
(38 pages)
Specifications of AT89S52
Flash (kbytes)
8 Kbytes
Max. Operating Frequency
24 MHz
Cpu
8051-12C
Max I/o Pins
32
Uart
1
Sram (kbytes)
0.25
Operating Voltage (vcc)
4.0 to 5.5
Timers
3
Isp
SPI
Watchdog
Yes
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11. Baud Rate Generator
1919D–MICRO–6/08
Timer 2 is selected as the baud rate generator by setting TCLK and/or RCLK in T2CON
5-2). 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
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 Modes 1 and 3 are determined by Timer 2’s overflow rate according to the fol-
lowing 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 timer operation is different for Timer 2 when it is
used as a baud rate generator. Normally, as a timer, it increments every machine cycle (at 1/12
the oscillator frequency). As a baud rate generator, however, it increments every state time (at
1/2 the oscillator frequency). The baud rate formula is 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
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
generator, T2EX can be used as an extra external interrupt.
Note that when Timer 2 is running (TR2 = 1) as a timer in the baud rate generator mode, TH2 or
TL2 should not be read from or written to. Under these conditions, the Timer is incremented
every state time, and the results of a read or write 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.
Modes 1 and 3 Baud Rates
Modes 1 and 3
-------------------------------------- -
Baud Rate
=
------------------------------------------------------------------------------------- -
32 x [65536-RCAP2H,RCAP2L)]
Oscillator Frequency
Figure
=
Timer 2 Overflow Rate
----------------------------------------------------------- -
11-1. This figure is valid only if RCLK or
Figure
16
11-1.
AT89S52
(Table
15