TMOD Special Function Register.

TMOD register

As we know there are 2 timer registers in 8051. Timer 0 and timer 1. Both of these registers use the same register called TMOD to set various timer operation modes.

TMOD is an 8-bit register, in which lower 4 bits are for Timer 0 and upper 4 bits are for Timer 1.

See table below. MSB ---- LSB
GATE
C/T
M1
M0
GATE
C/T
M1
M0
TIMER 1
TIMER 0

Bit Description:


BitTMOD Bit Function
7Gate -- OR gate enable bit which controls RUN/STOP of timer 1. Set to 1 by the program to enable the timer to run if bit TR1 in TCON is set and the signal on external interrupt is high. Cleared to 0 by the program to enable time to run if bit TR1 is set.
6C/T -- Set to 1 by the program to make timer 1 act as a counter by counting pulses from external input pins 3.5. Cleared to zero by the program to make timer act as a timer by counting internal frequency.
5M1 -- Timer/counter operating mode select bit 1. Set/cleared by the program to select mode.
4M0 -- Timer/counter operating mode select bit 0. Set/cleared by the program to select mode.
3Gate -- OR gate enable bit which controls RUN/STOP of timer 0. Set to 1 by the program to enable the timer to run if bit TR0 in TCON is set and the signal on external interrupt is high. Cleared to 0 by the program to enable time to run if bit TR0 is set.
2C/T -- Set to 1 by the program to make timer 0 act as a counter by counting pulses from external input pin 3.4. Cleared to zero by the program to make timer act as a timer by counting internal frequency.
1M1 -- Timer/counter operating mode select bit 1. Set/cleared by the program to select mode.
0M0 -- Timer/counter operating mode select bit 0. Set/cleared by the program to select mode.


M1
M0
MODE
OPERATING MODE
0
0
MODE 0
13 bit timer mode
8-bit timer/counter THx with TLx as 5-bit pre-scaler
0
1
MODE 1
16 bit timer mode.
16-bit timer/counter THx and TLx are cascaded with no pre-scaler.
1
0
MODE 2
8 bit auto reload.
8-bit auto reload-timer/counter  THx holds a value that’s to be reloaded in TLx each time it overflows.
1
1
MODE 3
Split timer mode












Comments

Post a Comment

Popular posts from this blog

General puprose registers in 8051.

Image
Well, in yesterday's podcast discussed on registers in 8051, two types of a register, general purpose registers are today's article all about. The general purpose registers are called as RAM memory in 8051. It has 128 bytes of memory for this general purpose registers. These general purpose registers are divided into 3 areas, those are  Banks. Bit addressable areas. scratchpad areas.                                     Let we discuss clearly, Banks    In this bank, 4 types of banks are there like  bank 0 bank 1 bank 2 bank 3 In each bank has 8 registers those are R0 to R7. All these general purpose registers are byte addressable registers. An image is shown in below for better understanding,                                     ...
Read more

TCON Special Function register.

Image
If a counter is programmed to be a timer, it will count the internal clock frequency of the 8051 oscillator 12d. As an example, if the crystal frequency 6 MHz, then the timer clock will have a frequency of 500kHz.   The timers may operate in any one of four modes that are determined by the mode bits. In that the timer control TCON it is a special function register. TCON:   Pin Description of TCON: Bit Symbol TCON Bit Function 7 TF1l Timer 1 Overflow flag. Set when timer rolls from all 1's to 0. Cleared when processor vectors to execute interrupt service routine located at program address 001Bh. 6 TR1l Timer 1 run control bit. Set to 1 by a program to enable the timer to count; cleared to 0 by the program to halt timer. 5 TF0 l Timer 0 Overflow flag. Set when timer rolls from all 1's to 0. Cleared when processor vectors to execute interrupt service routine located at program address 000Bh. 4 TR0l Timer 0 run control bit. Set to 1 by a program to ...
Read more