Philips P89LPC907 用户手册

2003 Dec 8     

42

Putting either Timer into Mode 0 makes it look like an 8048 Timer, which is an 8-bit Counter with a divide-by-32 prescaler. Figure 
5-4 shows Mode 0 operation.

In this mode, the Timer register is configured as a 13-bit register. As the count rolls over from all 1s to all 0s, it sets the Timer 
interrupt flag TFn. The count input is enabled to the Timer when TRn = 1. TRn is a control bit in the Special Function Register 
TCON (Figure 5-3). 

The 13-bit register consists of all 8 bits of THn and the lower 5 bits of TLn. The upper 3 bits of TLn are indeterminate and should 
be ignored. Setting the run flag (TRn) does not clear the registers.

Mode 0 operation is the same for Timer 0 and Timer 1. See Figure 5-4.

Mode 1 is the same as Mode 0, except that all 16 bits of the timer register (THn and TLn) are used. See Figure 5-5.

Mode 2 configures the Timer register as an 8-bit Counter (TLn) with automatic reload, as shown in Figure 5-6. Overflow from TLn 
not only sets TFn, but also reloads TLn with the contents of THn, which must be preset by software. The reload leaves THn 
unchanged. Mode 2 operation is the same for Timer 0 and Timer 1.

TAMOD - P89LPC907
Address: 8Fh

Not bit addressable
Reset Source(s): Any reset
Reset Value: 

xxx0xxx0B

TAMOD.7-1

-

Reserved for future use. Should not be set to 1 by user programs.

TAMOD.0

T0M2

Mode Select bit 2 for Timer 0. Used with T0M1 and T0M0 in the TMOD register to 
determine Timer 0 mode (P89LPC907).

TnM2-TnM0

Timer Mode

0 0 0

8048 Timer “TLn” serves as 5-bit prescaler. (Mode 0)

0 0 1

16-bit Timer/Counter “THn” and “TLn” are cascaded; there is no prescaler. (Mode 1)

0 1 0

8-bit auto-reload Timer/Counter. THn holds a value which is loaded into TLn when it 
overflows. (Mode 2)

0 1 1

Timer 0 is a dual 8-bit Timer/Counter in this mode. TL0 is an 8-bit Timer/Counter controlled 
by the standard Timer 0 control bits. TH0 is an 8-bit timer only, controlled by the Timer 1 
control bits (see text). Timer 1 in this mode is stopped. (Mode 3)

1 0 0

Reserved. User must not configure to this mode.

1 0 1

Reserved. User must not configure to this mode.

1 1 0

PWM mode (see section "Mode 6 - P89LPC907").

1 1 1

Reserved. User must not configure to this mode.

7

6

5

4

3

2

1

0

-

-

-

-

-

-

-

T0M2