CHAPTER 7
SOFTWARE PACKAGE

It is easy to achieve communications under MS/DOS by setting the RS422/RS485 board to COM1: and COM2:. The standard COM1: and COM2: communication statements are supported by most high level language such as: BASIC, PASCAL, C, ...etc.

In the following example, we will introduce users how to write an application program. In section 7.1, wwe will specify how to write high level language when the board is set to standard COM1: and COM:. Suppose your setting is not standard COM ports, the section 7.2 introduces the user how to write a driver. Section 7.3 provides how to use a SERIAL DRIVER to drive the RS422/RS485 board. The PCCOM software is a powerful package for serial communication, we will introduce it in section 7.4.


7.1 Use Standard COM Ports

Since BASIC language provides a buffer for communications, in the follows, we will demonstrate how to program under BASIC language. To start the communication task under BASIC, the statement

OPEN "COMn:speed, parity, ....... " AS ID

is used, then you can use the file ID to send or receive data from communication port.

In the following, we list send and receive programs which are written in the BASIC language.

1. Loopback Test (Basic Version)


2.File Transfer (Basic Version)



7.2 Write Your Own Driver

If you are going to set the port address thing other than standard COM ports, you must write a driver by yourself or use PCCOM software 9see section 7.4),    SERIAL DRIVER package (see section 7.3). In the following, we will demonstrate how to write a driver by yourself.

To write your own driver, the most important things are driver and receiver mode selection. When the adapter is set to always enable mode, the communication protocol is RS422. (Please refer the data book for 8250 chip to programming 8250 registers under RS422 mode)

When you select the RS485 mode, you may enable the driver for RTS or control register. We assume BASE=1A0, then

1. Enable RTS


2. Enable control register


The control register can be used to enable receiver.


A statement such as OUT BASE+7,3 will turn on both driver and receiver.

The PASCAL program listed below can be used to test the send and receiver functions.

uses
    crt ;

const
    p1 = $3f8 ;
    p2 = $2f8 ;

var
    delaytime : integer ;

procedure init(p,n : integer) ;
begin
    port[p+3] := $80
    port[p    ] := Lo(n)
    port[p+1] := Hi(n)
    port[p+3] := 3 ;
end ;
procedurd test ;
const
    baud1 : array[1..3]  of integer = (    96,    12,          2) ;
    baud2 : array[1..3] of     word = (1200,9600,57600) ;
var
    tx,rx dir stat, testloop,baudindex,i : integer ;
    b1,b2 : byte ;
    c : char ;
begin
    init (p1,96)
    init (p2,96)

    port[p2+4] := 3; { /RTS = Low }
    port[p2+7] := 0;
    port[p1+7] := 2; {Enable RX    }
    port[p1+4] :=0;

    for i := 1 to 20 do
    begin
        repeat
            b1 := random(256)
        until bq <> b2;
        port[p2] := b1;
        delay(delaytime);
        b2 := port[p1];
        writeln(b1:4,b2:12);
    end;
    c := readkey;
end;

begin {main}
    clrscr;
    randomize;
    delaytime := 100;
    write('Enter delay time (1..1000) (ms) : ');
    readln(delaytime);
    test;
    writeln('Done.......');
end.


7.3 Under Serial Driver

The SERIAL DRIVER can be used to drive your RS422 or RS485 port. To drive RS485 or RS422 you need not give the interrupt vector address and active status, because the RS422/RS485 board does not support an interrupt vector. It is easily to control the RS422 mode under the SERIAL DRIVER. However, if you set the RS485 mode, yo must take over the RTS signal or control register. The MCR (byte 1) of I/O control can be used to set RTS to enable the driver (see SERIAL DRIVER chapter 6). To enable the driver by the control register, please use OUT BASE+7 statement.


7.4 Under PCCOM Software Package

The PCCOM software can be used to drive your RS422, you need not give interrupt vector address and active status, because the RS422/RS485 board does not support an interrupt vector. It is easy to control the RS422 mode under PCCOM. However, if you set the RS485 mode, you must take over the RTS signal or control register. The OUT BASE+4 statement can be used to set RTS to enable the driver. To enable the driver by the  control register, please use OUT BASE+7 statement.