Siemens SIMATIC TI500 Bedienungsanleitung PDF herunterladen (Seite 54)

Modbus Commands

C-5

TIWAY I Gateway User Manual

• Terminology

is another area in which differences occur

. Some of the

differences in terms are given in T

able C-3.

able C-3

Ter

minology Dif

ferences

Modbus-based PLCs SIMATIC TI PLCs

Coil Discrete output (Y) or Control Relay (C)

Input Register Word Image Register (WX/WY)

Holding Register Variable Memory (V-memory)

Slave Secondary Node

P/C (Programmable Controller) PLC

Function code Primitive

Modbus TIWAY I

Disabled (coil) Forced

Enabled (coil) Unforced

The

TIW

Y I Gateway uses the absolute position of the data for the address.

That is, if you want to address the 3066th coil, then that is the address you

pass with the command (as hexadecimal value BF

A). The maximum address

is 65535 (FFFF hex). For example, if you want to access 1000 coils starting

at the 703rd coil, the Function Code 01 would be as follows:

01 01 02 BF 03 E8 0C E8

Modbus imposes a buffer size limit of 256 bytes. Because of this restriction,

TIWA

Y I Gateway requests have been limited to the following values.

Function Code Quantity

2000 coils

2000 discrete inputs

125 output registers

125 input registers

800 coils

100 registers

The

command checking will reject requests for data greater than the limits

shown above. What the checking does

not

do is check the request against

the available PLC memory

. When a request goes beyond the memory of a

particular PLC, the command will be rejected by the PLC and the host

computer will be notified by the Exception Code 02.

Addressing

Addr

ess Limits

1 2 ... 49 50 51 52 53 54 55 56 57 58 59 ... 93 94

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