Datasheet

Philips Semiconductors Product data
P80C3xX2; P80C5xX2;
P87C5xX2
80C51 8-bit microcontroller family
4K/8K/16K/32K ROM/OTP, low voltage (2.7 to 5.5 V),
low power, high speed (30/33 MHz)
2003 Jan 24
15
GATE C/T M1
M0 GATE C/T
M1 M0
BIT SYMBOL FUNCTION
TMOD.3/ GATE Gating control when set. Timer/Counter “n” is enabled only while “INTn
” pin is high and
TMOD.7 “TRn” control pin is set. when cleared Timer “n” is enabled whenever “TRn” control bit is set.
TMOD.2/ C/T
Timer or Counter Selector cleared for Timer operation (input from internal system clock.)
TMOD.6 Set for Counter operation (input from “Tn” input pin).
M1 M0 OPERATING
0 0 8048 Timer: “TLn” serves as 5-bit prescaler.
0 1 16-bit Timer/Counter: “THn” and “TLn” are cascaded; there is no prescaler.
1 0 8-bit auto-reload Timer/Counter: “THn” holds a value which is to be reloaded
into “TLn” each time it overflows.
1 1 (Timer 0) TL0 is an 8-bit Timer/Counter controlled by the standard Timer 0 control bits.
TH0 is an 8-bit timer only controlled by Timer 1 control bits.
1 1 (Timer 1) Timer/Counter 1 stopped.
SU01580
TIMER 1 TIMER 0
Not Bit Addressable
TMOD Address = 89H Reset Value = 00H
76543 2 1 0
Figure 1. Timer/Counter 0/1 Mode Control (TMOD) Register
INTn Pin
Timer n
Gate bit
TRn
TLn
(5 Bits)
THn
(8 Bits)
TFn Interrupt
Control
C/T = 0
C/T = 1
SU01618
OSC
÷ d*
Tn Pin
*d = 6 in 6-clock mode; d = 12 in 12-clock mode.
Figure 2. Timer/Counter 0/1 Mode 0: 13-Bit Timer/Counter