STC micro STC8A8K64D4 Series - Example of Fine-Tuning to Get a User Frequency of 3 Mhz

STC8A8K64D4 Series Manual
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6.2.5 Example of fine-tuning to get a user frequency of 3MHz
To get a frequency of 3MHz, you can use the method of 24MHz divided by 8.
Select the internal IRC operating frequency as 24MHz firstly when downloading the ISP, as shown in the figure below.
Then select the internal IRC as the clock source in the code and use the CLKDIV register to divide by 8.
C language code
// Operating frequency for test is 24MHz
#include "reg51.h"
#include "intrins.h"
#define CKSEL (*(unsigned char volatile xdata *)0xfe00)
#define CLKDIV (*(unsigned char volatile xdata *)0xfe01)
#define HIRCCR (*(unsigned char volatile xdata *)0xfe02)
#define XOSCCR (*(unsigned char volatile xdata *)0xfe03)
#define IRC32KCR (*(unsigned char volatile xdata *)0xfe04)
sfr P_SW2 = 0xba;
sfr IRTRIM = 0x9f;
sfr P0M1 = 0x93;
sfr P0M0 = 0x94;
sfr P1M1 = 0x91;
sfr P1M0 = 0x92;
sfr P2M1 = 0x95;
sfr P2M0 = 0x96;
sfr P3M1 = 0xb1;
sfr P3M0 = 0xb2;
sfr P4M1 = 0xb3;
sfr P4M0 = 0xb4;
sfr P5M1 = 0xc9;
sfr P5M0 = 0xca;
void main()
{
P0M0 = 0x00;
P0M1 = 0x00;
P1M0 = 0x00;
P1M1 = 0x00;
P2M0 = 0x00;
P2M1 = 0x00;