IS80C51 Datasheet, PDF (15/43 Pages) Integrated Silicon Solution, Inc – CMOS SINGLE CHIP 8-BIT MICROCONTROLLER

IS80C51
IS80C31
ISSI ^®
Mode 1:
Mode 1 is the same as Mode 0, except that the Timer
register is run with all 16 bits. The clock is applied to the
combined high and low timer registers (TL1/TH1). As clock
pulses are received, the timer counts up: 0000H, 0001H,
0002H, etc. An overflow occurs on the FFFFH-to-0000H
overflow flag. The timer continues to count. The overflow
flag is the TF1 bit in TCON that is read or written by
software (see Figure 9).
Mode 2:
Mode 2 configures the Timer register as an 8-bit Counter
(TL1) with automatic reload, as shown in Figure 10.
Overflow from TL1 not only sets TF1, but also reloads TL1
with the contents of TH1, which is preset by software. The
reload leaves the TH1 unchanged. Mode 2 operation is the
same for Timer/Counter 0.
Mode 3:
Timer 1 in Mode 3 simply holds its count. The effect is the
same as setting TR1 = 0. Timer 0 in Mode 3 establishes TL0
and TH0 as two separate counters. The logic for Mode 3 on
Timer 0 is shown in Figure 11. TL0 uses the Timer 0 control
bits: C/T, GATE, TR0, INT0, and TF0. TH0 is locked into a
timer function (counting machine cycles) and over the use
of TR1 and TF1 from Timer 1. Thus, TH0 now controls the
Timer 1 interrupt.
Mode 3 is for applications requiring an extra 8-bit timer or
counter. With Timer 0 in Mode 3, the IS80C51/31 can
appear to have three Timer/Counters. When Timer 0 is in
Mode 3, Timer 1 can be turned on and off by switching it out
of and into its own Mode 3. In this case, Timer 1 can still be
used by the serial port as a baud rate generator or in any
application not requiring an interrupt.
OSC
DIVIDE 12
T1 PIN
GATE
INT0 PIN
C/T = 0
C/T = 1
TR1
TL1
(8 BITS)
CONTROL
TF1
RELOAD
TH1
(8 BITS)
Figure 10. Timer/Counter 1 Mode 2: 8-Bit Auto-Reload
INTERRUPT
OSC
DIVIDE 12
1/12 FOSC
1/12 FOSC
T0 PIN
GATE
C/T = 0
C/T = 1
TR0
TL0
(8 BITS)
CONTROL
TF0
INTERRUPT
INT0 PIN
1/12 FOSC
TR1
TH0
(8 BITS)
CONTROL
TF1
INTERRUPT
Figure 11. Timer/Counter 0 Mode 3: Two 8-Bit Counters
Integrated Silicon Solution, Inc. — 1-800-379-4774
15
MC003-1D
11/19/98