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DirectNET Host

Communications Prog.

6–2

DirectNET Host Communications Programs

Why do you need a communications program?

Since DirectNET is a master / slave network, the master station must initiate

requests for network data transfers. If you’re using a host as the master station, you

will need to use a communications program written with the DirectNET protocol.

The communications program used with a hosted network is more complex than the

simple RLL instructions used with the other configurations, but the concept is the

same. The host is the DirectNET master and must use a DirectNET protocol

communications program to initiate all network requests to read or write data. These

communication programs can be written in many different languages, such as

BASIC, C, etc. and must include the appropriate DirectNET commands.

Here’s an example of a DirectNET program. (This is just part of the program.)

DirectNET Program in BASIC

10 REM Program to read X0–X7 from a DL405 PLC

20 REM

30 REM Define all variables

40 REM

50 REM Change the slave address in HEX at line 60 if required.

60 SLAVEADDRESS=&H1

70 DATATYPE$=CHR$(&H32)

80 DATAADDR$=CHR$(&H30)+CHR$(&H31)+CHR$(&H30)+CHR$(&H31)

90 COMPLETEBLK$=CHR$(&H30)+CHR$(&H30)

100 PARTBLK$=CHR$(&H30)+CHR$(&H32)

110 MASTERADDR$=CHR$(&H30)+CHR$(&H30)

120 NORMAL$=CHR$(&H4E)

130 SLAVEADDR$=HEX$(SLAVEADDRESS)

140 IF LEN(SLAVEADDR$)<2 THEN SLAVEADDR$=”0”+SLAVEADDR$

150 OFFSETADDR$=CHR$(&H20+SLAVEADDRESS)

NOTE: This manual does not show you how to build communications programs that

manage the data storage and communications ports. You should check the

documentation that came with your programming software to determine the

appropriate techniques to solve these requirements.

The Master

Initiates Requests

DirectNET

Programs

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