Exploring STC 8051 Microcontrollers – Coding

Using PCA as a Software Timer

We have already seen how the PCA module doubles as timer in the capture examples. However, unlike actual hardware timers, we would have to use some software tricks and keep certain things in mind.

Code

 include "STC8xxx.h"
#include "BSP.h"
 
#define T_Load         (1000000L / 12 / 2)
 
unsigned int value = T_Load;
 
void setup(void);
 
void PCA_ISR(void)          
interrupt 7
{
  clear_PCA_0_flag;
  PCA0_load_value(value);
  P55_toggle;
  value += T_Load;
}
 
void main(void)
{
 
  setup();
  
  while(1)
  {
  };
}
 
void setup(void)
{
  CLK_set_sys_clk(IRC_24M, 24, MCLK_SYSCLK_no_output, MCLK_out_P54);
 
  P55_open_drain_mode;
  
  PCA_pin_option(0x10);
  
  PCA_setup(PCA_continue_counting_in_idle_mode, PCA_clk_sys_clk_div_12);
  
  PCA_0_mode(PCA_16_bit_software_timer);
    
  PCA_load_counter(0);
  PCA0_load_value(T_Load);
  
  _enable_PCA_0_interrupt;
  _enable_global_interrupt;
  
  PCA_start_counter;
}

Schematic

Explanation

This example uses the same concepts as in the high-speed pulse output example and yes, again it is a simple onboard LED blinking example. Between the two examples almost everything is same.   

The system clock is set to 1MHz.

CLK_set_sys_clk(IRC_24M, 24, MCLK_SYSCLK_no_output, MCLK_out_P54); 

PCA is setup with just as in the past example except for the clock prescalar and mode of operation. In this example, the PCA clock is set to 83.3kHz and software timer mode is selected. Note that since no PCA input-output channel is needed in this example, it doesn’t matter which pin arrangement is initialized.

 PCA_pin_option(0x10);
  
PCA_setup(PCA_continue_counting_in_idle_mode, PCA_clk_sys_clk_div_12);
  
PCA_0_mode(PCA_16_bit_software_timer);
    
PCA_load_counter(0);
PCA0_load_value(T_Load);
  
_enable_PCA_0_interrupt;
_enable_global_interrupt;
  
PCA_start_counter;

The desired LED blinking frequency is 1Hz and so the PCA0 is loaded with the following count value.

Since we are toggling the onboard LED, every half second, it will change its state and so the toggling frequency is 1 Hz.  

Note there is no operation in the main loop.

Demo

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17 comments

  • hello.
    this is a very good effort to document all and still share with us. thank you very much.
    I have one doubt . which programming tool are you using ?

  • Hi, I am trying to understand the STC15w408as chip, and found this site after weeks of searching for something that sets the output of the GPIO pins to a different state. I have a the 28 pin stc15w and have connected it up with a FTDI board and can write to it using PlatformIO. The thing is, the GPIO ports if just switched on or do a reset they are in the HIGH state and I am trying to make them LOW when you do a reset.
    Is your BSP code doing this and for what port or GPIO pin is it setting? I could change your P52 and P55 in your SETUP to the GPIO pins on my development board but not under standing the BSP Code.
    Wonder if you get this post? but any help would be gratefully received.

  • Hi,
    How Purchase the development board. Please,give the purchase link for this Development board.

  • How To read and write string data using IAP into memory

    • void IAP_erase(unsigned int address)
      {
      IAP_CONTR = 0x80; //?? IAP
      IAP_TPS = 12;
      // IAP_CONTR = IAP_WT;
      IAP_CMD = IAP_erase_command;
      IAP_address(address);
      IAP_trigger;
      _nop_();
      _nop_();
      _nop_();
      IAP_clear;
      }

      void IAP_send_string(unsigned int uc_send_addr,unsigned char *uca_send_string,unsigned int uc_number_of_bytes)
      {
      unsigned int buff_cntr=0;
      do
      {
      IAP_CONTR = 0x80; //?? ISP/IAP ??
      IAP_TPS = (unsigned char)(11509200 / 1000000L); //??????
      IAP_CMD = IAP_write_command;

      // IAP_CMD = IAP_write_command;
      IAP_ADDRH = uc_send_addr / 256; //??????(??????????????)
      IAP_ADDRL = uc_send_addr % 256; //??????
      IAP_DATA = uca_send_string[buff_cntr]; //???? ISP_DATA,????????????
      IAP_trigger;//IAP_TRIG();
      _nop_();
      _nop_();
      _nop_();
      uc_send_addr++;
      // uca_send_string++;
      buff_cntr++;

      IAP_clear;
      delay_ms(8);
      }while(–uc_number_of_bytes);
      }

      void IAP_read_string(unsigned int uc_read_addr,unsigned char *data_read,unsigned int uc_number_of_bytes)
      {
      unsigned int buff_cntr=0;
      do{
      IAP_CONTR = 0x80; //?? ISP/IAP ??
      IAP_TPS = (unsigned char)(11059200 / 1000000L); //??????
      IAP_CMD = IAP_read_command;

      // IAP_CMD = IAP_read_command;
      IAP_ADDRH = uc_read_addr / 256; //??????(??????????????)
      IAP_ADDRL = uc_read_addr % 256; //??????
      IAP_trigger;//IAP_TRIG(); //?? 5AH,?? A5H ? ISP/IAP ?????,
      //???????
      //?? A5H ?, ISP/IAP ?????????
      //CPU ?? IAP ???,?????????
      _nop_();
      _nop_();
      _nop_();
      data_read[buff_cntr] = IAP_DATA; //???????
      uc_read_addr++;
      // data_read++;
      buff_cntr++;

      IAP_clear;
      delay_ms(8);
      }while(–uc_number_of_bytes);
      }

      stores only last byte to all bytes of flash memory sector… memory sector selected is 0xF600

  • Hi, I am using STC MCU since 10 years. Tech support is ZERO. but they are low cost, very stable. Now I have a problem when the chip that I used is obsolete. Now start to use STC8C2K64S4-28I-LQFP32 but no stc8Cxx.h file, I am using stc8Hxx.h file which compiles but in some stage freeze, the existing firmware. With stc8hxx.h file I can compile STC8F2K64S4-28I-LQFP32 and works not bad
    .
    I wrote them many times for the stc8Cxx.h file never got answer. Where Can I find that file?
    Thank you

  • Hi. Can you explain how to use I2C in the slave mode ?

    • I tried STC8G1K08A i2c in slave mode. Doesn’t work (no response). It does not enter interrupt, even on a start condition (everything according to the code in the documentation). I also tried master mode – it works.

  • 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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