CPU Specifications
and Operation
4–39
CPU Specifications and Operation
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’s still fairly simple. Basically, MODBUS also separates
the data types by address ranges as well. So 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:
S 484 Mode
S 584/984 Mode
We recommend that you use the 584/984 addressing mode if your 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.
S Discrete – X, SP, Y, CR, S, T, C (contacts)
S 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 addresses (as required). The table below shows the exact
equation used for each group of data.
DL05 Memory Type
QTY
(Dec.)
PLC Range
(Octal)
MODBUS
Address Range
(Decimal)
484 Mode
Address
584/984
Mode
Address
MODBUS
Data Type
For Discrete Data Types ... Convert PLC Addr. to Dec. + Start of Range + Appropriate Mode Address
Inputs (X) 256 X0 – X377 2048 – 2303 1001 10001 Input
Special Relays (SP) 512 SP0 – SP777 3072 – 3583 1001 10001 Input
Outputs (Y) 256 Y0 – Y377 2048 – 2303 1 1 Coil
Control Relays (CR) 512 C0 – C777 3072 – 3583 1 1 Coil
Timer Contacts (T) 128 T0 – T177 6144 – 6271 1 1 Coil
Counter Contacts (CT) 128 CT0 – CT177 6400 – 6527 1 1 Coil
Stage Status Bits (S) 256 S0 – S377 5120 – 5375 1 1 Coil
For Word Data Types .... Convert PLC Addr. to Dec. + Appropriate Mode Address
Timer Current Values (V) 128 V0 – V377 0 – 127 3001 30001 Input Reg.
Counter Current Values (V) 128 V1000 – V1177 512 – 639 3001 30001 Input Reg
V Memory, user data (V) 3200 V1400 – V7377 768 – 3839 4001 40001 Hold Reg.
V Memory, non-volatile (V) 128 V7400 – V7577 3840 – 3967 4001 40001 Hold Reg.
V Memory, system (V) 256 V7600 – V7777 3968 – 4095 4001 40001 Hold Reg.
If Your MODBUS
Host Software
Requires an
Address ONLY
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