AT89C51AC3-RDTIM datasheet(71/141 Pages) ATMEL

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AT89C51AC3

4383A–8051–10/04

Table 31. TMOD Register

TMOD (S:89h)

Timer/Counter Mode Control Register

Reset Value = 0000 0000b

7654

3210

GATE1

C/T1#

M11

M01

GATE0

C/T0#

M10

M00

Bit

Number

Bit

Mnemonic

Description

7GATE1

Timer 1 Gating Control Bit

Clear to enable Timer 1 whenever TR1 bit is set.

Set to enable Timer 1 only while INT1# pin is high and TR1 bit is set.

6C/T1#

Timer 1 Counter/Timer Select Bit

Clear for Timer operation: Timer 1 counts the divided-down system clock.

Set for Counter operation: Timer 1 counts negative transitions on external pin T1.

5M11

Timer 1 Mode Select Bits

M11 M01

Operating mode

Mode 0: 8-bit Timer/Counter (TH1) with 5-bit prescaler (TL1).

Mode 1: 16-bit Timer/Counter.

Mode 2: 8-bit auto-reload Timer/Counter (TL1)

(1)

Mode 3: Timer 1 halted. Retains count

Reloaded from TH1 at overflow.

4M01

3GATE0

Timer 0 Gating Control Bit

Clear to enable Timer 0 whenever TR0 bit is set.

Set to enable Timer/Counter 0 only while INT0# pin is high and TR0 bit is set.

2C/T0#

Timer 0 Counter/Timer Select Bit

Clear for Timer operation: Timer 0 counts the divided-down system clock.

Set for Counter operation: Timer 0 counts negative transitions on external pin T0.

1M10

Timer 0 Mode Select Bit

M10 M00

Operating mode

Mode 0: 8-bit Timer/Counter (TH0) with 5-bit prescaler (TL0).

Mode 1: 16-bit Timer/Counter.

Mode 2: 8-bit auto-reload Timer/Counter (TL0)

(2)

Mode 3: TL0 is an 8-bit Timer/Counter

TH0 is an 8-bit Timer using Timer 1’s TR0 and TF0 bits.

Reloaded from TH0 at overflow.

M00

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