Mapping two bits in coil or in discrete input

C

Thread Starter

cb singh

Hi,

I have one problem. In our case, each transducer have four states i.e.
00 - Normal
01 - Reverse
10 - Flashing
11 - Free

This will needs two bits to encode it. And standard MOBBUS has single bits (coils and discrete input) and word (registers) access. So, how to map it in MODBUS.

Please suggest me.

-CB Singh
[email protected]
HBLNIFE Power System Ltd.
Hyderabad,
INDIA.
 
Can you describe you problem more clearly? What type of PLC or transducer you use?
Anyway, you can use two discrete address (two coils) for one transducer or use one word.
 
Yaah I am explaning my problem in more details.
In our system no standard PLC is there. We have two processor based systems.
One is connected with field which continuously read the field data and store in memory. Another processor based system will read / write that system. We want to use modbus between them.
Field data consist of points of railway tracks i.e. around 100. And each point of railway track consist of four values. that is
Normal, Reverse, Free, Moving.
So, I mapped it into 00-normal, 01-reverse, 10-free and 11-moving.
So we need two bits per point. O.k.
So, in one byte contains 4 points.
But in MODBUS protocol to read coils(02) and read discrete input(01) has one bit per coil or discrete input.
So, for example if I want to read/write points from 1 to 10 then how to read it.

Please suggest me.
-cbsingh
[email protected]
 
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