Greeting. I have a problem with usart on pic16f690.
The compiler is HiTech C.
I enable receive interrupt for the USART, however it doesn’t work.
It just only do transmit character b to PC, when I have transmitted character c from PC to MCU.
Could someone give me suggestion or point out which routine is wrong ?

here is my code
--------------------------------------------------
#include < pic16f685.h >
#include "usart.h"
#include "delay.h"
void Init(void);
extern unsigned char status_flag@0x26;
static bit flag1 @ ((unsigned)&status_flag*8)+0;
//*****************************************************
//Main() - Main Routine
//*****************************************************
void main()
{
Init();
while(1)
{
DelayMs(200);
if(flag1==1)
{ putch('a');
GIE=1;
}
else putch('b');
DelayMs(200);
}
}
void Init()
{
OPTION =0;
TRISC =0;
TRISC4 =1;
TRISB =0;
OSCCON = 0b01100000;
OSCTUNE = 0b00000000;
ANSEL = 0b00000000;
C1ON =0;
C2ON =0;
CCP1CON =0;
ADCON1 = 0B01010000;
ADCON0 =0;
GODONE =0;
TMR1CS =0; //
T1CKPS1 =0; //
T1CKPS0 =0; //
TRISB5 =1;
TXSTA=0b00100000;
RCSTA=0b10010000;
SCKP=0;//
SPBRG=25;
SYNC =0;
BRGH =1;
BRG16 =0;
INTCON=0;
PIE1=0;
GIE=1;
PEIE=1;
TXIF=0;
TXIE=0;
RCIF=0;
RCIE=1;
CCP1IE=0;
TMR2IE=0;
TMR1IE=0;
flag1=0;
}
//**********************************************
//interrupt routine
//**********************************************
static void interrupt
isr(void) // interrupt function -
{
unsigned char abc;
GIE=0;
if(RCIF==1&&RCIE==1)
{
abc=RCREG;
if(abc=='c')
{
flag1=1;
}
else flag1=0;
}
}
------------------------------------------------
usart.h code
#ifndef _SERIAL_H_
#define _SERIAL_H_

#define BAUD 9600
#define FOSC 4000000L
#define NINE 0 /* Use 9bit communication? FALSE=8bit */

#define DIVIDER ((int)(FOSC/(16UL * BAUD) -1))
#define HIGH_SPEED 1

#if NINE == 1
#define NINE_BITS 0x40
#else
#define NINE_BITS 0
#endif

#if HIGH_SPEED == 1
#define SPEED 0x4
#else
#define SPEED 0
#endif

#if defined(_16F87) || defined(_16F88)
#define RX_PIN TRISB2
#define TX_PIN TRISB5
#else
#define RX_PIN TRISC7
#define TX_PIN TRISC6
#endif

/* Serial initialization */
#define init_comms()\
RX_PIN = 1; \
TX_PIN = 1; \
SPBRG = DIVIDER; \
RCSTA = (NINE_BITS|0x90); \
TXSTA = (SPEED|NINE_BITS|0x20)

void putch(unsigned char);
unsigned char getch(void);
unsigned char getche(void);

#endif
--------------------------------
usart.c
#include < pic.h >
#include < stdio.h >
#include "usart.h"

void
putch(unsigned char byte)
{
/* output one byte */
while(!TXIF) /* set when register is empty */
continue;
TXREG = byte;
}

unsigned char
getch() {
/* retrieve one byte */
while(!RCIF) /* set when register is not empty */
continue;
RCIF=0;
return RCREG;
}

unsigned char
getche(void)
{
unsigned char c;
putch(c = getch());
return c;
}