AT89S52-24AC Atmel, AT89S52-24AC Datasheet - Page 12
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AT89S52-24AC
Manufacturer Part Number
AT89S52-24AC
Description
IC MCU 8K FLASH 24MHZ 44-TQFP
Manufacturer
Atmel
Series
89Sr
Datasheet
1.AT89S52-24AU.pdf
(38 pages)
Specifications of AT89S52-24AC
Core Processor
8051
Core Size
8-Bit
Speed
24MHz
Connectivity
UART/USART
Peripherals
WDT
Number Of I /o
32
Program Memory Size
8KB (8K x 8)
Program Memory Type
FLASH
Ram Size
256 x 8
Voltage - Supply (vcc/vdd)
4 V ~ 5.5 V
Oscillator Type
Internal
Operating Temperature
0°C ~ 70°C
Package / Case
44-TQFP, 44-VQFP
Lead Free Status / RoHS Status
Contains lead / RoHS non-compliant
Eeprom Size
-
Data Converters
-
Available stocks
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10. Timer 2
10.1
10.2
12
Capture Mode
Auto-reload (Up or Down Counter)
AT89S52
Timer 2 is a 16-bit Timer/Counter that can operate as either a timer or an event counter. The
type of operation is selected by bit C/T2 in the SFR T2CON (shown in
three operating modes: capture, auto-reload (up or down counting), and baud rate generator.
The modes are selected by bits in T2CON, as shown in
registers, TH2 and TL2. In the Timer function, the TL2 register is incremented every machine
cycle. Since a machine cycle consists of 12 oscillator periods, the count rate is 1/12 of the oscil-
lator frequency.
Table 10-1.
In the Counter function, the register is incremented in response to a 1-to-0 transition at its corre-
sponding external input pin, T2. In this function, the external input is sampled during S5P2 of
every machine cycle. When the samples show a high in one cycle and a low in the next cycle,
the count is incremented. The new count value appears in the register during S3P1 of the cycle
following the one in which the transition was detected. Since two machine cycles (24 oscillator
periods) are required to recognize a 1-to-0 transition, the maximum count rate is 1/24 of the
oscillator frequency. To ensure that a given level is sampled at least once before it changes, the
level should be held for at least one full machine cycle.
In the capture mode, two options are selected by bit EXEN2 in T2CON. If EXEN2 = 0, Timer 2 is
a 16-bit timer or counter which upon overflow sets bit TF2 in T2CON. This bit can then be used
to generate an interrupt. If EXEN2 = 1, Timer 2 performs the same operation, but a 1-to-0 transi-
tion at external input T2EX also causes the current value in TH2 and TL2 to be captured into
RCAP2H and RCAP2L, respectively. In addition, the transition at T2EX causes bit EXF2 in
T2CON to be set. The EXF2 bit, like TF2, can generate an interrupt. The capture mode is illus-
trated in
Timer 2 can be programmed to count up or down when configured in its 16-bit auto-reload
mode. This feature is invoked by the DCEN (Down Counter Enable) bit located in the SFR
T2MOD (see
count up. When DCEN is set, Timer 2 can count up or down, depending on the value of the
T2EX pin.
RCLK +TCLK
Figure
X
0
0
1
Table
Timer 2 Operating Modes
10-1.
10-2). Upon reset, the DCEN bit is set to 0 so that timer 2 will default to
CP/RL2
X
X
0
1
TR2
1
1
1
0
Table
MODE
16-bit Auto-reload
16-bit Capture
Baud Rate Generator
(Off)
10-1. Timer 2 consists of two 8-bit
Table
5-2). Timer 2 has
1919D–MICRO–6/08