Seneca S6001-RTU, User Manual

Page: 205 / 210

USER MANUAL – Z-TWS4/Z-PASS2-S/S6001-RTU
205
21 Access to Straton variables
The aim of this chapter is to explain how an application (typically, web-based) can access the variables of
the Straton Soft-PLC running on Z-TWS4/Z-PASS2-S/S6001-RTU.
Currently, there are two ways to access Straton variables:

direct access to Straton shared-memory

access by means of CGI
The main differences between the two methods is that the first requires developing a C program, running
on the Device, typically invoked by the lighttpd web server, while the second does not require any changes
in the Device FW, provided that the currently supported CGIs are used.
21.1 Shared Memory
Straton Workbench lets you define a shared-memory area and tell which PLC variables shall be put in it.
For each variable in the shared-memory, the Workbench lets you define the following properties:

Symbol: the name of a Straton variable defined elsewhere (Global Variables, Retain Variables etc.)

Offset: the offset in the shared-memory

Size: the variable size, in bytes

Format: the kind of variable, i.e. “signed integer”

Mode: if the variable is an Input, an Output or an In/Out (from the Straton point of view)