W78E054D Datasheet, PDF (49/89 Pages) List of Unclassifed Manufacturers – 8-bit microcontroller

W78E054D/W78E052D Data Sheet
14 PROGRAMMABLE TIMERS/COUNTERS
The W78E054D/W78E052D series have Three 16-bit programmable timer/counters. A machine cycle
equals 12 or 6 oscillator periods, and it depends on 12T mode or 6T mode that the user configured
this device.
14.1 Timer/Counters 0 & 1
W78E054D/W78E052D has two 16-bit Timer/Counters. Each of these Timer/Counters has two 8 bit
registers which form the 16 bit counting register. For Timer/Counter 0 they are TH0, the upper 8 bits
register, and TL0, the lower 8 bit register. Similarly Timer/Counter 1 has two 8 bit registers, TH1 and
TL1. The two can be configured to operate either as timers, counting machine cycles or as counters
counting external inputs.
When configured as a "Timer", the timer counts clock cycles. The timer clock can be programmed to
be thought of as 1/12 of the system clock. In the "Counter" mode, the register is incremented on the
falling edge of the external input pin, T0 in case of Timer 0, and T1 for Timer 1. The T0 and T1 inputs
are sampled in every machine cycle at C4. If the sampled value is high in one machine cycle and low
in the next, then a valid high to low transition on the pin is recognized and the count register is incre-
mented. Since it takes two machine cycles to recognize a negative transition on the pin, the maximum
rate at which counting will take place is 1/24 of the master clock frequency. In either the "Timer" or
"Counter" mode, the count register will be updated at C3. Therefore, in the "Timer" mode, the recog-
nized negative transition on pin T0 and T1 can cause the count register value to be updated only in
the machine cycle following the one in which the negative edge was detected.
The "Timer" or "Counter" function is selected by the " ^C/T " bit in the TMOD Special Function Register.
Each Timer/Counter has one selection bit for its own; bit 2 of TMOD selects the function for Tim-
er/Counter 0 and bit 6 of TMOD selects the function for Timer/Counter 1. In addition each Tim-
er/Counter can be set to operate in any one of four possible modes. The mode selection is done by
bits M0 and M1 in the TMOD SFR.
14.2 Time-Base Selection
W78E054D/W78E052D provides users with two modes of operation for the timer. The timers can be
programmed to operate like the standard 8051 family, counting at the rate of 1/12 of the clock speed.
This will ensure that timing loops on W78E054D/W78E052D and the standard 8051 can be matched.
This is the default mode of operation of the W78E054D/W78E052D timers.
14.2.1 Mode 0
In Mode 0, the timer/counter is a 13-bit counter. The 13-bit counter consists of THx (8 MSB) and the
five lower bits of TLx (5 LSB). The upper three bits of TLx are ignored. The timer/counter is enabled
when TRx is set and either GATE is 0 or ^INTx is 1. When ^{C/ T} is 0, the timer/counter counts clock
cycles; when ^{C/ T} is 1, it counts falling edges on T0 (Timer 0) or T1 (Timer 1). For clock cycles, the
time base be 1/12 speed, and the falling edge of the clock increments the counter. When the 13-bit
value moves from 1FFFh to 0000h, the timer overflow flag TFx is set, and an interrupt occurs if ena-
bled.
14.2.2 Mode 1
Mode 1 is similar to Mode 0 except that the counting register forms a 16-bit counter, rather than a 13-
bit counter. This means that all the bits of THx and TLx are used. Roll-over occurs when the timer
moves from a count of 0FFFFh to 0000h. The timer overflow flag TFx of the relevant timer is set and if
enabled an interrupt will occur. The selection of the time-base in the timer mode is similar to that in
Mode 0. The gate function operates similarly to that in Mode 0.
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Publication Release Date: Jun 9, 2015
Revision A13