Tuesday, March 24, 2015

Addressing S7-300 Modules

Addressing S7-300 Modules

Slot Numbers
The slot numbers in the rack of an S7-300 simplify addressing in the
S7-300  environment. The position of the module in the rack determine the first
address on a module.

Slot 1
Power supply. This is the first slot by default.
A power supply module is not absolutely essential. An S7-300  can also be
supplied with 24V directly.

Slot 2
Slot for the CPU.

Slot 3
Logically reserved for an interface module (IM) for multi-tier configurations using
expansion racks. Even if no IM is installed, it must be included for addressing
You can physically reserve the slot (such as for installing an IM at a later date) if
you insert a DM370 dummy module.

Slots 4-11
Slot 4 is the first slot that can be used for I/O modules, communications
processors (CP) or function modules (FM).
Addressing examples:
• A DI module in slot 4 begins with the byte address 0 .
• The top LED of a DO module in slot 6 is called Q8.0 .

Four byte addresses are reserved for each slot. When 16-channel DI/DO
modules are used, two byte addresses are lost in every slot!

DI/DO Addressing in Multi-Tier Configurations

Multi-Tier Configurations
The slots also have fixed addresses in a multi-tier configuration.

• Q7.7 is the last bit of a 32-channel DO module plugged into slot 5 of rack 0.
• IB105 is the second byte of a DI module in slot 6 of rack 3.
• QW60 is the first two bytes of a DO module in slot 11 of rack 1.
• ID80 is all four bytes of a 32-channel DI module in slot 8 in rack 2.

Module Address Overview

Address  Overview
Views the I/O addresses of the station configured. Select: View -> Address Overview …

R Rack number
S Slot number of the relevant module
DPRelevant only when Distributed Peripherals (I/O) are used
IF Interface module ID when programming the M7 system (in C++).

Variable Addressing

Slot dependent Addressing 
The modules are assigned fixed slot-dependent addresses with the S7-300  (CPUs without DP interface) and S7-400 (without hardware configuration).

Variable Addressing
With the S7-300  (CPUs with integrated DP interface) and with the S7-400 you can assign parameters to the starting addresses of the modules.

What to Do
When you double-click a digital or an analog module, the parameter assignment
screen is opened. After you choose the "Addresses" tab, you can cancel
"System selection". You can now define the starting address in the "Start" box. If
the address is already used, an error message is triggered.
Part process images can be defined only in the S7-400 . That way, specific
inputs and outputs (such as time-critical signals) can be combined into one
group. A system function triggers the updating of a part process image in the
user program.

After a CPU memory reset, the parameters, and therefore also the addresses
are lost. This means that the slot-dependent addresses of the S7-300  or the
default addresses of the S7-400  are valid once more.