AT90LS4433-4AI datasheet(39/126 Pages) ATMEL

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AT90S/LS4433

1042H–AVR–04/03

• Bits 2, 1, 0 – CS12, CS11, CS10: Clock Select1, Bits 2, 1, and 0

The Clock Select1 bits 2, 1, and 0 define the prescaling source of Timer/Counter1.

The Stop condition provides a Timer Enable/Disable function. The prescaled CK modes

are scaled directly from the CK Oscillator clock. If the external pin modes are used for

Timer/Counter0, transitions on PD5/(T1) will clock the counter even if the pin is config-

ured as an output. This feature can give the user software control of the counting.

Timer/Counter1 – TCNT1H and

TCNT1L

This 16-bit register contains the prescaled value of the 16-bit Timer/Counter1. To

ensure that both the High and Low Bytes are read and written simultaneously when the

CPU accesses these registers, the access is performed using an 8-bit temporary regis-

ter (TEMP). This temporary register is also used when accessing OCR1 and ICR1. If the

main program and interrupt routines perform access to registers using TEMP, interrupts

must be disabled during access from the main program (and from interrupt routines if

interrupts are allowed from within interrupt routines).

• TCNT1 Timer/Counter1 Write

When the CPU writes to the High Byte TCNT1H, the written data is placed in the TEMP

bined with the byte data in the TEMP Register, and all 16 bits are written to the TCNT1

Timer/Counter1 Register simultaneously. Consequently, the High Byte TCNT1H must

be accessed first for a full 16-bit register write operation.

• TCNT1 Timer/Counter1 Read

When the CPU reads the Low Byte TCNT1L, the data of the Low Byte TCNT1L is sent

to the CPU and the data of the High Byte TCNT1H is placed in the TEMP Register.

When the CPU reads the data in the High Byte TCNT1H, the CPU receives the data in

Table 12. Clock 1 Prescale Select

CS12

CS11

CS10

Description

Stop, the Timer/Counter1 is stopped.

001

010

CK/8

011

CK/64

100

CK/256

101

CK/1024

External Pin T1, falling edge

External Pin T1, rising edge

Bit

15141312

$2D ($4D)

MSB

TCNT1H

$2C ($4C)

LSB

TCNT1L

543

210

Read/Write

R/W

R/WR/W

Initial Value

000

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