8-bit microcontroller with accelerated two-clock 80C51 core
8.17 Timers/counters 0 and 1
The P89LPC933/934/935/936 has two general purpose counter/timers which are upward
compatible with the standard 80C51 Timer 0 and Timer 1. Both can be configured to
operate either as timers or event counter. An option to automatically toggle the T0 and/or
T1 pins upon timer overflow has been added.
In the ‘timer’ function, the register is incremented every machine cycle.
In the ‘counter’ function, the register is incremented in response to a 1-to-0 transition at its
corresponding external input pin, T0 or T1. In this function, the external input is sampled
once during every machine cycle.
Timer 0 and Timer 1 have five operating modes (modes 0, 1, 2, 3 and 6). Modes 0, 1, 2
and 6 are the same for both timers/counters. Mode 3 is different.
8.17.1 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. In this mode, the timer register is configured as a 13-bit
register. Mode 0 operation is the same for Timer 0 and Timer 1.
8.17.2 Mode 1
Mode 1 is the same as Mode 0, except that all 16 bits of the timer register are used.
8.17.3 Mode 2
Mode 2 configures the timer register as an 8-bit counter with automatic reload. Mode 2
operation is the same for Timer 0 and Timer 1.
8.17.4 Mode 3
When Timer 1 is in Mode 3 it is stopped. Timer 0 in Mode 3 forms two separate 8-bit
counters and is provided for applications that require an extra 8-bit timer. When Timer 1 is
in Mode 3 it can still be used by the serial port as a baud rate generator.
8.17.5 Mode 6
In this mode, the corresponding timer can be changed to a PWM with a full period of
256 timer clocks.
8.17.6 Timer overflow toggle output
Timers 0 and 1 can be configured to automatically toggle a port output whenever a timer
overflow occurs. The same device pins that are used for the T0 and T1 count inputs are
also used for the timer toggle outputs. The port outputs will be a logic 1 prior to the first
timer overflow when this mode is turned on.
8.18 RTC/system timer
The P89LPC933/934/935/936 has a simple RTC that allows a user to continue running an
accurate timer while the rest of the device is powered-down. The RTC can be a wake-up
or an interrupt source. The RTC is a 23-bit down counter comprised of a 7-bit prescaler
and a 16-bit loadable down counter. When it reaches all logic 0s, the counter will be
reloaded again and the RTCF flag will be set. The clock source for this counter can be
either the CPU clock (CCLK) or the XTAL oscillator, provided that the XTAL oscillator is
Product data sheet
All information provided in this document is subject to legal disclaimers.
Rev. 8 — 12 January 2011
© NXP B.V. 2011. All rights reserved.
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