AT89C55WD-24PU Atmel, AT89C55WD-24PU Datasheet - Page 11

• Manufacturer Part Number: AT89C55WD-24PU
• Description: IC 8051 MCU FLASH 20K 40DIP
• Manufacturer: Atmel
• Series: 89Cr

Specifications of AT89C55WD-24PU

• Core Processor: 8051
• Core Size: 8-Bit
• Speed: 24MHz
• Connectivity: UART/USART
• Peripherals: WDT
• Number Of I /o: 32
• Program Memory Size: 20KB (20K x 8)
• Program Memory Type: FLASH
• Ram Size: 256 x 8
• Voltage - Supply (vcc/vdd): 4.5 V ~ 5.5 V
• Oscillator Type: Internal
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 40-DIP (0.600", 15.24mm)
• Processor Series: AT89x
• Core: 8051
• Data Bus Width: 8 bit
• Data Ram Size: 256 B
• Interface Type: UART
• Maximum Clock Frequency: 24 MHz
• Number Of Programmable I/os: 32
• Number Of Timers: 3
• Operating Supply Voltage: 4 V to 6 V
• Maximum Operating Temperature: + 85 C
• Mounting Style: Through Hole
• 3rd Party Development Tools: PK51, CA51, A51, ULINK2
• Minimum Operating Temperature: - 40 C
• Package: 40PDIP
• Device Core: 8051
• Family Name: 89C
• Maximum Speed: 24 MHz
• Cpu Family: AT89
• Device Core Size: 8b
• Frequency (max): 24MHz
• Total Internal Ram Size: 256Byte
• # I/os (max): 32
• Number Of Timers - General Purpose: 3
• Operating Supply Voltage (typ): 5V
• Operating Supply Voltage (max): 5.5V
• Operating Supply Voltage (min): 4V
• Instruction Set Architecture: CISC
• Operating Temp Range: -40C to 85C
• Operating Temperature Classification: Industrial
• Mounting: Through Hole
• Pin Count: 40
• Package Type: PDIP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Eeprom Size: -
• Data Converters: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

12. Timer 2
12.1
12.2
1921D–MICRO–6/08
Capture Mode
Auto-reload (Up or Down Counter)
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
Timer 2 consists of two 8-bit 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 oscillator frequency.
Table 12-1.
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
0
0
1
X
Timer 2 Operating Modes
12-1.
Table
12-2). 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)
5-2.
AT89C55WD
Table
5-2). Timer 2 has
11