AT89C55WD Atmel Corporation, AT89C55WD Datasheet - Page 15
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AT89C55WD
Manufacturer Part Number
AT89C55WD
Description
Manufacturer
Atmel Corporation
Datasheet
1.AT89C55WD.pdf
(35 pages)
Specifications of AT89C55WD
Flash (kbytes)
20 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 6.0
Timers
3
Watchdog
Yes
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Figure 13-1. Timer 2 in Baud Rate Generator Mode
14. Programmable Clock Out
1921D–MICRO–6/08
T2EX PIN
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"
AT89C55WD
"1"
÷
SMOD1
RCLK
TCLK
÷
16
16
Figure
CLOCK
CLOCK
Rx
Tx
14-1. This
15