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Philips Semiconductors
TIMERS 0 AND 1
TAMOD
Address: 8Fh
Not bit addressable
Reset Source(s): Any reset
Reset Value:
xxx0xxx0B
BIT
SYMBOL
TAMOD.7-5
-
TAMOD.4
T1M2
TAMOD.3-1
-
TAMOD.0
T0M2
TnM2-TnM0
0 0 0
0 0 1
0 1 0
0 1 1
1 0 0
1 0 1
1 1 0
1 1 1
Mode 0
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
7-4 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 and either TnGATE = 0 or INTn = 1. (Setting TnGATE
= 1 allows the Timer to be controlled by external input INTn, to facilitate pulse width measurements). TRn is a control bit in the
Special Function Register TCON (Figure 7-3). The TnGATE bit is in the TMOD register.
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 7-4. There are two different GATE bits, one for Timer 1
(TMOD.7) and one for Timer 0 (TMOD.3).
Mode 1
Mode 1 is the same as Mode 0, except that all 16 bits of the timer register (THn and TLn) are used. See Figure 7-5.
2003 Dec 8
7
6
-
FUNCTION
Reserved for future use. Should not be set to 1 by user programs.
Mode Select bit 2 for Timer 1. It is used with T1M1 and T1M0 in the TMOD register to
determine Timer 1 mode.
Reserved for future use. Should not be set to 1 by user programs.
Mode Select bit 2 for Timer 0. It is used with T0M1 and T0M0 in the TMOD register to
determine Timer 0 mode.
Timer Mode
8048 Timer "TLn" serves as 5-bit prescaler. (Mode 0)
16-bit Timer/Counter "THn" and "TLn" are cascaded; there is no prescaler.(Mode 1)
8-bit auto-reload Timer/Counter. THn holds a value which is loaded into TLn when it
overflows. (Mode 2)
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)
Reserved. User must not configure to this mode.
Reserved. User must not configure to this mode.
PWM mode (see section "Mode 6").
Reserved. User must not configure to this mode.
Figure 7-2: Timer/Counter Auxiliary Mode Control register (TAMOD)
5
4
-
-
T1M2
42
User's Manual - Preliminary -
P89LPC920/921/922
3
2
1
-
-
-
0
T0M2
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