Interfacing the Serial/RS-232 Port

Interfacing the Serial / RS232 Port V5.0
Part 3 : Programming (PC's)
Polling or Interrupt Driven
When writing a communications program you have two methods available to you. You can poll
the UART, to see if any new data is available or you can set up an interrupt handler to remove the data
from the UART when it generates a interrupt. Polling the UART is a lot slower method, which is very
CPU intensive thus can only have a maximum speed of around 34.8 KBPS before you start losing data.
Some newer Pentium Pro's may be able to achieve better rates that this. The other option is using a
Interrupt handler, and that's what we have used here. It will very easily support 115.2K BPS, even on
low end computers.
Termpoll.c - A sample Comms Program using Polling
Para que comprendais el codigo fuente que se muestra a continuacion
es recomendable que se revisen conceptos vistos en practicas anteriores.
#include
#include
#include
#define PORT1 0x3F8
/* Defines Serial Ports Base Address */
/* COM1 0x3F8 */
/* COM2 0x2F8 */
/* COM3 0x3E8 */
/* COM4 0x2E8 */
void main(void)
{
int c;
int ch;
outportb(PORT1 + 1 , 0); /* Turn off interrupts - Port1 */
Interfacing the Serial / RS232 Port V5.0 Page 22