Automation Direct D2-DCM, Руководство пользователя

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C–7
C–7
Using the D2–DCM with MODBUS
Data Communications Module, 2nd Edition, 2/03
Some host software packages do 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 also separates the data
types by address ranges as well. This 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 addressing modes may be available in your host software
package. These are:
D
484 Mode
D
584/984 Mode
We recommend that you use the 584/984 addressing mode if the host software allows
you 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 the address depends on the type of PLC data you are using. The PLC memory
types are split into two categories for this purpose.
D
Discrete – X, GX, SP, Y, CR, S, T (contacts), C (contacts)
D
Word – V, Timer current value, Counter current value
In either case, you basically convert the PLC octal address to decimal and add the
appropriate MODBUS starting address (as required). The following tables show the exact
range used for each group of data.
Discrete Data Types
Memory Type PLC Range
(Octal)
Address
(484 Mode)
Address
(584/984 Mode) Data Type
Global Inputs (GX) GX0–GX1746 1001 – 1999 10001–10999 Input
GX1747 – GX3777 ––– 11000–12048 Input
Inputs (X) X0 – X1777 ––– 12049 – 13072 Input
Special Relays (SP) SP0– SP777 ––– 13073 – 13584 Input
Global Outputs (GY) GY0– GY3777 1 – 2048 1 – 2048 Output
Outputs (Y) Y0 – Y1777 2049 – 3072 2049 – 3072 Output
Control Relays (CR) C0 – C3777 3073 – 5120 3073 – 5120 Output
Timer Contacts (T) T0 – T377 6145 – 6400 6145 – 6400 Output
Counter Contacts (CT) CT0 – CT377 6401 – 6656 6401 – 6656 Output
Stage Status Bits (S) S0 – S1777 5121 – 6144 5121 – 6144 Output
If the Host Software
Requires an Address
ONLY