Exploring STC 8051 Microcontrollers – Coding

Using Timer 4 as Time-base Generator

The very basic use of a timer is to use it for time-base generation. By time-base generation, I mean that we use a timer as a free-running timer and without using any of its interrupts.

Code

 #include "STC8xxx.h"
#include "BSP.h"
 
void setup(void);
 
void main(void)

  setup();
  
  while(1)
  {
      if(TMR4_get_counter() >= 0x9E58)
      {
        P55_high;
      }
      else
      {
        P55_low;
      }
  };
}
 
void setup(void)
{
  CLK_set_sys_clk(IRC_24M, 24, MCLK_SYSCLK_no_output, MCLK_out_P54);
  
  P55_open_drain_mode;
  
  TMR4_setup(TMR4_sysclk, \
             TMR4_clk_prescalar_12T, \
             TMR4_no_clk_out);
  
  TMR4_load_counter_16(0x3CB0);
  TMR4_start;
}

Schematic

Explanation

For this demo, onboard LED is used as the demo is a simple LED blinking. The desired LED blink rate is 1.67Hz (about 600ms).

The system clock is set to 1MHz. Everything related to internal hardware timing is dependent on system clock and so its selection is very important. The system clock is set to 1MHz as the required blink rate is very small. Every system clock tick is, therefore, 1µs.

 CLK_set_sys_clk(IRC_24M, 24, MCLK_SYSCLK_no_output, MCLK_out_P54); 

Now let’s see how the timer is configured. Firstly, timer 4 is used as it is one of the simplest timers. Obviously, this timer is working in 16-bit auto-reload mode (Mode 0) as no other mode of operation is available for it.

 TMR4_setup(TMR4_sysclk, \
           TMR4_clk_prescalar_12T, \
           TMR4_no_clk_out);
  
TMR4_load_counter_16(0x3CB0);
TMR4_start;

As we can see the timer is fed with internal system clock (1MHz). This is further scaled down by a factor of 12, i.e., the timer is ticking at:

All 16-bit timers start counting from a bottom value to a fixed top value of 65535 (0xFFFF) counts. A timer’s internal counter overflows after exceeding the top value and then rolls over or repeats counting from its bottom value. The bottom value is 0 (0x0000) unless some other value is assigned in the code. Thus, unlike the top value, the bottom value can be changed. In this example, the bottom value is 15536 (0x3CB0). This, in effect, help us achieve 50000 counts.

65536 – 15536 = 50000 counts

Now, we want to equally divide the on and off times of the LED and so the 50000 counts are divided into two halves, each 25000 counts individually. Thus, in the main loop, the timer’s counter count is polled.

 if(TMR4_get_counter() >= 0x9E58)
{
  P55_high;
}
else
{
  P55_low;
}

If the count is greater than or equal to 40536 (0x9E58), P55 is held high or else it is held low. Thus, from 15536 count to 40535 count (40535 – 15536 = 24999), the pin’s state is low and from 40536 count to 65535 count (65535 – 40536 = 24999), the pin state is high.

Demo

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6 comments

  • Thanks for these tutorials. I’m getting back into STCmicro coding now, having left them alone for the past several years. Back then I only used the STC89C52RC (and C54RD) but this time I’m also using the more powerful STC15 and STC8 types. Your blogs provide a wealth of useful information.

  • Hello,

    You have done great job with all these tutorials. I am an electronics engineer trying to learn some new stuff. I am located in Greece , Europe and I would like to purchase the development board that you are using and download some datasheets in English if possible but I cannot find them anywhere. Could you please help me?

  • i always get excited when you release new tutorials ,you are really doing a great job i wish i could write code and develop libraries like you.

  • Well, this is very nice and thorough tutorial indeed, many thanks!
    Unfortunately I doubt there is good any reason to learn the STC platform beyond curiosity.
    The STC 8051, although pretty evolved from the original 8051 ISA, does not offer anything crucial to justify the relatively high price of these micros and development tools along with certain cumbersomeness of this ancient platform.
    They simply can not compete even with the legacy Cortex M0 in any way. I am even not aware about any affordable debugger/emulator for them.
    All in all, I would never recommend anybody to start learning/using any 8051 without some very good reason to do so.

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