AT89LP428 Atmel Corporation, AT89LP428 Datasheet - Page 41

• Manufacturer Part Number: AT89LP428
• Manufacturer: Atmel Corporation

Specifications of AT89LP428

• Flash (kbytes): 4 Kbytes
• Max. Operating Frequency: 25 MHz
• Cpu: 8051-1C
• Max I/o Pins: 30
• Spi: 1
• Uart: 1
• Sram (kbytes): 0.75
• Eeprom (bytes): 512
• Self Program Memory: IAP
• Operating Voltage (vcc): 2.4 to 5.5
• Timers: 3
• Isp: SPI/OCD
• Watchdog: Yes

11. Enhanced Timer 0 and Timer 1 with PWM
3654A–MICRO–8/09
The AT89LP428/828 has two 16-bit Timer/Counters, Timer 0 and Timer 1, with the
following features:
Timer 0 and Timer 1 have similar modes of operation. As timers, they increase every clock cycle
by default. Thus, the registers count clock cycles. Since a clock cycle consists of one oscillator
period, the count rate is equal to the oscillator frequency. The timer rate can be prescaled by a
value between 1 and 16 using the Timer Prescaler (see
share the same prescaler.
As counters, the timer registers are incremented in response to a 1-to-0 transition at the corre-
sponding input pins, T0 or T1. The external input is sampled every clock 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 the cycle following the one in which the transition was
detected. Since 2 clock cycles are required to recognize a 1-to-0 transition, the maximum count
rate is 1/2 of the oscillator frequency. There are no restrictions on the duty cycle of the input sig-
nal, but it should be held for at least one full clock cycle to ensure that a given level is sampled at
least once before it changes.
Furthermore, the Timer or Counter functions for Timer 0 and Timer 1 have four operating modes:
variable width timer, 16-bit auto-reload timer, 8-bit auto-reload timer, and split timer. The control
bits C/T in the Special Function Register TMOD select the Timer or Counter function. The bit
pairs (M1, M0) in TMOD select the operating modes.
Table 11-1.
Name
TCON
TMOD
TL0
TL1
TH0
TH1
TCONB
RL0
RL1
RH0
RH1
• Two 16-bit timer/counters with 16-bit reload registers
• Two independent 8-bit precision PWM outputs with 8-bit prescalers
• UART or SPI baud rate generation using Timer 1
• Output pin toggle on timer overflow
• Split timer mode allows for three separate timers (two 8-bit, one 16-bit)
• Gated modes allow timers to run/halt based on an external input
Timer 0/1 Register Summary
Address
8CH
8DH
8AH
8BH
88H
89H
91H
92H
93H
94H
95H
Control
Mode
Timer 0 low-byte
Timer 1 low-byte
Timer 0 high-byte
Timer 1 high-byte
Mode
Timer 0 reload low-byte
Timer 1 reload low-byte
Timer 0 reload high-byte
Timer 1 reload high-byte
Purpose
Table 6-2 on page
AT89LP428/828
Bit-Addressable
23). Both Timers
Y
N
N
N
N
N
N
N
N
N
N
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