If Your Modbus Host Software Requires An Address Only - Automationdirect.com DirectLOGIC DL205 Series User Manual

Chapter 4: System Design and Configuration

If Your Modbus Host Software Requires an Address ONLY

1
Some host software does not allow you to specify the Modbus data type and address. Instead,
you specify an address only. This method requires another step to determine the address, but
it is not difficult. Basically, Modbus separates the data types by address ranges as well. So this
2
means an address alone can actually describe the type of data and location. This is often
referred to as "adding the offset". One important thing to remember here is that two different
3
addressing modes may be available in your host software package. These are:
• 484 Mode
4
• 584/984 Mode
We recommend that you use the 584/984 addressing mode if your host software allows you
5
to choose. This is because the 584/984 mode allows access to a higher number of memory
locations within each data type. If your software only supports 484 mode, then there may be
some PLC memory locations that will be unavailable. The actual equation used to calculate
6
the address depends on the type of PLC data you are using. The PLC memory types are split
into two categories for this purpose.
7
• Discrete – X, GX, SP, Y, R, S, T, CT (contacts), C (contacts)
• Word – V, Timer current value, Counter current value
8
In either case, you basically convert the PLC octal address to decimal and add the appropriate
Modbus addresses (as required). The table below shows the exact equation used for each
9
group of data.
10
DL260 Memory Type
11
Global Inputs (GX)
12
Inputs (X)
Special Relays (SP)
13
Global Outputs (GY)
Outputs (Y)
14
Control Relays (C)
Timer Contacts (T)
Counter Contacts (CT)
A
Stage Status Bits (S)
B
C
D
4–38
DL205 User Manual, 4th Edition, Rev. B
Discrete Data Types
Address Range
PLC Range (Octal)
(484 Mode)
GX0 – GX1746 1001 – 1999
GX1747 – GX3777
X0 – X1777
SP0 – SP777
GY0 – GY3777 1 – 2048
Y0 – Y1777 2049 – 3072
C0 – C3777 3073 – 5120
T0 – T377 6145 – 6400
CT0 – CT377 6401 – 6656
S0 – S1777 5121 – 6144
Address Range
(584/984 Mode)
10001 – 10999
--- 11000 – 12048
--- 12049 – 13072
--- 13073 – 13584
1 – 2048
2049 – 3072
3073 – 5120
6145 – 6400
6401 – 6656
5121 – 6144
Modbus Data Type
Input
Input
Input
Input
Output
Output
Output
Output
Output
Output