MCLREをONにしているので、リセット回路を追加する必要がある。

PIC16F628A_led_blink.c

#define _XTAL_FREQ 4000000L

// PIC16F628A Configuration Bit Settings

// 'C' source line config statements

// CONFIG
#pragma config FOSC = INTOSCIO  // Oscillator Selection bits (INTOSC oscillator: I/O function on RA6/OSC2/CLKOUT pin, I/O function on RA7/OSC1/CLKIN)
#pragma config WDTE = OFF       // Watchdog Timer Enable bit (WDT disabled)
#pragma config PWRTE = ON       // Power-up Timer Enable bit (PWRT enabled)
#pragma config MCLRE = ON      // RA5/MCLR/VPP Pin Function Select bit (RA5/MCLR/VPP pin function is digital input, MCLR internally tied to VDD)
#pragma config BOREN = ON       // Brown-out Detect Enable bit (BOD enabled)
#pragma config LVP = OFF        // Low-Voltage Programming Enable bit (RB4/PGM pin has digital I/O function, HV on MCLR must be used for programming)
#pragma config CPD = OFF        // Data EE Memory Code Protection bit (Data memory code protection off)
#pragma config CP = OFF         // Flash Program Memory Code Protection bit (Code protection off)

// #pragma config statements should precede project file includes.
// Use project enums instead of #define for ON and OFF.

#include <xc.h>

void main(void) {
    PCON        = 0b00001000; // 4MHz
    OPTION_REG  = 0b00000000; // PORTB Pull-up Enable(bit7)
    CMCON       = 0b00000111; // CM<2:0> = 111. Comparators Off
    VRCON       = 0b00000000;
    TRISA       = 0b00010000; // RA<4:0> as outputs, TRISA<5> always reas as '1'
    TRISB       = 0b00000000; 
    
    PORTA = 0x00;
    PORTB = 0x00;

    while(1) {
        RB0 = 1;
        __delay_ms(500);
        RB0 = 0;
        __delay_ms(500);
    }
    return;
}