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Philips Semiconductors
User’s Manual - Preliminary -
P89LPC901/902/903
TIMERS 0 AND 1
2003 Dec 8 47
Mode 3
When Timer 1 is in Mode 3 it is stopped. The effect is the same as setting TR1 = 0.
Timer 0 in Mode 3 establishes TL0 and TH0 as two separate 8-bit counters. The logic for Mode 3 on Timer 0 is shown in Figure
5-7. TL0 uses the Timer 0 control bits: TR0 and TF0. TH0 is locked into a timer function (counting machine cycles) and takes
over the use of TR1 and TF1 from Timer 1. Thus, TH0 now controls the “Timer 1” interrupt.
Mode 3 is provided for applications that require an extra 8-bit timer.
Note: When Timer 0 is in Mode 3, Timer 1 can be turned on and off by switching it into and out of its own Mode 3. It can still be
used by the serial port as a baud rate generator (P89LPC903 only), or in any application not requiring an interrupt.
Mode 6 - P89LPC901
In this mode, Timer 0 can be changed to a PWM with a full period of 256 timer clocks (see Figure 5-8). Its structure is similar to
mode 2, except that:
• TF0 is set and cleared in hardware;
• The low period of the TF0 is in TH0, and should be between 1 and 254, and;
• The high period of the TF0 is always 256-TH0.
• Loading TH0 with 00h will force the T0 pin high, loading TH0 with FFh will force the T0 pin low.
Note that an interrupt can still be enabled on the low to high transition of TF0, and that TF0 can still be cleared in software as in
any other modes.
Figure 5-3: Timer/Counter Control register (TCON)
TCON
Address: 88h
Bit addressable
Reset Source(s): Any reset
Reset Value: 00000000B
BIT SYMBOL FUNCTION
TCON.7 TF1 Timer 1 overflow flag. Set by hardware on Timer overflow. Cleared by hardware when the
interrupt is processed, or by software.
TCON.6 TR1 Timer 1 Run control bit. Set/cleared by software to turn Timer 1 on/off.
TCON.5 TF0 Timer 0 overflow flag. Set by hardware on Timer/Counter overflow. Cleared by hardware
when the processor vectors to the interrupt routine, or by software. (except in mode 6, see
above, when it is cleared in hardware)
TCON.4 TR0 Timer 0 Run control bit. Set/cleared by software to turn Timer/Counter 0 on/off.
TCON.3 - Reserved for future use. Should not be set to 1 by user programs.
TCON.2 - Reserved for future use. Should not be set to 1 by user programs.
TCON.1 - Reserved for future use. Should not be set to 1 by user programs.
TCON.0 - Reserved for future use. Should not be set to 1 by user programs.
76543210
TF1 TR1 TF0 TR0 - - - -