Transmission

PCI-COM422/4 Manual

RS422 transmission is simple to implement. The AUTO feature of the PCI-COM422/4 card automatically enables the transmitter when data is ready to send so no software enabling is required. The following software example is for non-AUTO operation.

To transmit a string of data, the transmitter must first check Bit 5 of the Line Status Register at Base Address +5. That bit is the transmitter-holding-register-empty flag. If it is high, the transmitter has sent the data. The process of checking the bit until it goes high followed by a write is repeated until no data remains.

The following C code fragment demonstrates this process:

outportb(BASEADDR +4, inportb(BASEADDR +4)0x02); /*Set RTS bit without altering states of other bits*/

while(data[i]); /*While there is data to send*/

{

while(!(inportb(BASEADDR +5)&0x20)); /*Wait until transmitter is empty*/ outportb(BASEADDR,data[i]);

i++;

}

outportb(BASEADDR +4, inportb(BASEADDR +4)&0xFD); /*Reset RTS bit without altering states of other bits*/

Page 5-4

Manual MPCICOM422-4.E1b