AT89S52 Atmel Corporation, AT89S52 Datasheet - Page 16

• Manufacturer Part Number: AT89S52
• Manufacturer: Atmel Corporation

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

Figure 11-1. Timer 2 in Baud Rate Generator Mode
12. Programmable Clock Out
16
T2EX PIN
AT89S52
OSC
T2 PIN
÷
2
TRANSITION
DETECTOR
A 50% duty cycle clock can be programmed to come out on P1.0, as shown in
pin, besides being a regular I/O pin, has two alternate functions. It can be programmed to input
the external clock for Timer/Counter 2 or to output a 50% duty cycle clock ranging from 61 Hz to
4 MHz (for a 16-MHz operating frequency).
To configure the Timer/Counter 2 as a clock generator, bit C/T2 (T2CON.1) must be cleared and
bit T2OE (T2MOD.1) must be set. Bit TR2 (T2CON.2) starts and stops the timer.
The clock-out frequency depends on the oscillator frequency and the reload value of Timer 2
capture registers (RCAP2H, RCAP2L), as shown in the following equation.
In the clock-out mode, Timer 2 roll-overs will not generate an interrupt. This behavior is similar to
when Timer 2 is used as a baud-rate generator. It is possible to use Timer 2 as a baud-rate gen-
erator and a clock generator simultaneously. Note, however, that the baud-rate and clock-out
frequencies cannot be determined independently from one another since they both use
RCAP2H and RCAP2L.
NOTE: OSC. FREQ. IS DIVIDED BY 2, NOT 12
C/T2 = 0
C/T2 = 1
Clock-Out Frequency
EXEN2
TR2
CONTROL
CONTROL
RCAP2H
TH2
EXF2
=
RCAP2L
------------------------------------------------------------------------------------ -
4 x [65536-(RCAP2H,RCAP2L)]
TL2
Oscillator Frequency
INTERRUPT
TIMER 2
÷
2
"1"
"1"
TIMER 1 OVERFLOW
"0"
"0"
"0"
"1"
÷
÷
SMOD1
RCLK
TCLK
16
16
Figure
1919D–MICRO–6/08
CLOCK
CLOCK
Rx
Tx
12-1. This