W79E201 Datasheet, PDF (42/87 Pages) Winbond – 8-BIT MICROCONTROLLER

W79E201
Table 7. Priority structure of interrupts
SOURCE
External Interrupt 0
ADC Interrupt
Timer 0 Overflow
External Interrupt 1
Timer 1 Overflow
Serial Port
Timer 2 Overflow
Watchdog Timer
FLAG
IE0
ADCI
TF0
IE1
TF1
RI + TI
TF2 + EXF2
WDIF
VECTOR ADDRESS
0003h
006Bh
000Bh
0013h
001Bh
0023h
002Bh
0063h
PRIORITY LEVEL
1(highest)
2
3
4
5
6
7
8 (lowest)
11. PROGRAMMABLE TIMERS/COUNTERS
The W79E201 has three 16-bit programmable timer/counters and one programmable Watchdog timer.
The Watchdog timer is operationally quite different from the other two timers.
11.1 Timer/Counters 0 & 1
The Timer/Counters 0/1 have 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 or 1/4 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 incremented. 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 recognized 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
Timer/Counter 0 and bit 6 of TMOD selects the function for Timer/Counter 1. In addition each
Timer/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.
Time-Base Selection
The W79E201 gives the user 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 the W79E201 and the standard 8051 can be matched. This is the default mode of
operation of the W79E201 timers. The user also has the option to count in the turbo mode, where the
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