PCA0MD &= ~0x40;

error C202: 'PCA0MD': undefined identifier

   WDTCN = 0xDE;                       // Disable watchdog timer
   WDTCN = 0xAD;

error C202: 'WDTCN': undefined identifier
          error C202: 'WDTCN': undefined identifier

#include <C8051F020.h>

Error C231 Redefinition

printf("Interrupt 0 occured. \n");

#include <stdio.h>
#include <string.h>
#include <REG52.H>

void fputchar (unsigned char c1)
{
  SBUF = c1;
    while (!TI);
      TI = 0;
}

void main(void)
{
  idata char src[] = "Output string";
  idata char *psrc = src;
  int len, cnt;

     SCON = 0x50;
      TH1 = 0xFD;
    TMOD |= 0x20;
      TR1 = 1;
       TI = 0;
      len = strlen(src);

for (cnt = 0; cnt < len; cnt++)
{
   fputchar(*psrc);
   psrc++;
}

while(1);

SBUF = c1;

NAME PROCS
      T2CON EQU 0C8h
      RCAP2H EQU 0CBh
      RCAP2L EQU 0CAh
CSEG AT 0
USING 0
JMP start
SerINT:
ORG 23h
JBC RI, RCV
RETI
RCV:
MOV P1, SBUF
RETI
;——————————————
start:
MOV P1, #0h
MOV SCON, #50h
CLR T2CON.0
CLR T2CON.1
SETB T2CON.4
SETB T2CON.5
MOV RCAP2H, #0FFh
MOV RCAP2L, #0B2h
SETB T2CON.2
SETB ES
SETB EA
SETB TI
SJMP $