Communication
Memory Area Section 4.1
Memory Area
Memory Area Description
Introduction
In Safety Mode, the Safety CPU rejects all write requests to the following memory areas:
%M or %Q (0x register)
%MW or %QW (4x register)
EFB data
However, because it may be necessary for you to be able to write data to the Safety PLC, the memory is divided into a Safety and an unrestricted part, allowing you to write in %M as well as in
%MW.
Safety Memory Description
The Safety memory area is write protected for any other device.
NOTE: The write access is controlled inside the CPU because some communications, for example with the HMI or with other PLCs (Safety or non-Safety), are not configured in the Safety PLC with
Unity Pro XLS and therefore cannot be checked in the Unity Pro XLS configuration.
Write Protection Description
To prevent other devices from writing to the Safety memory area, there is a blocking mechanism.
The PLC does not execute any write command and returns an error code.
Unrestricted Memory Area Description
The unrestricted memory area (UMA) is a specially dedicated memory area for bits and words which is not write protected. It has the following characteristics:
It is located at the beginning of the complete memory range.
Its size can be configured in Unity Pro XLS.
Its values cannot be used directly but by using specific function blocks.
Configuring the Unrestricted Memory Area
You can configure the size of your unrestricted memory area in Unity Pro XLS in the CPU configuration with the following limits:
In %MW, the limit is
the last word in the unrestricted area or
0 if this area is not used.
104
33003879 10/2017
Communication
In %M, the limit is
a multiple of 16 and the last %M in the unrestricted area or
0 if it is not used.
NOTE: Configure the unrestricted memory area first and confirm that the configured area is large enough. If this part of the memory must be modified later, all addresses must be changed.
CAUTION
RISK OF CORRUPT PROJECT
Check that the size of the unrestricted memory area is correctly stored in the Quantum Safety
CPU after the download of the PLC application. To do so, you must read the system words
%SW110 and %SW111 (for instance using the animation table) and compare them with the configured values in your application.
Failure to follow these instructions can result in injury or equipment damage.
Using Data from the Unrestricted Memory Area
To perform Safety Functions, you are only allowed to process data stored in the Safety memory area. If it is necessary to get access to the Safety Functions, you are allowed to use data from the unrestricted memory data. However, for Safety reasons, you cannot process them directly. Instead you must transfer data from the unrestricted memory area to the Safety memory area in order for
Safety Functions to use these data.
You can find a detailed procedure for transferring data from the unrestricted to the Safety memory area in the chapter "Using Data from the Unrestricted Memory Area" in the Unity Pro XLS
Operating Mode Manual Safety PLC Specifics .
Description of the Safety Move Function Blocks
Because you are not able to work with the values located in the unrestricted memory area directly, there are the following 2 function blocks enabling you to transfer data from the unrestricted memory area to the Safety memory:
S_SMOVE_BIT to get access to bits
S_SMOVE_WORD to get access to words
The variables from the unrestricted memory area are connected to the input of the function block, and its output is connected to a Safety variable. Direct addresses cannot be used because they are interpreted as INT . The WORD to be moved must be configured in the unrestricted memory area. If the actual value is not within the range, the output is set to 0 and the error is indicated.
Additional inputs are used to control how the function blocks transfer the data to the outputs in case some data can only be used together in the same cycle.
NOTE: It is good practice to use an appropriate naming convention for variables from the unrestricted memory area and to comment them accordingly. This eases the audit of your SIL3 project.
33003879 10/2017
105
Communication
The user can use data in the safety application by implementing a verification protocol (for example, send a word and its complement and then check the consistency in the application, copy the word in a new location and then reread the value, etc.).
Write Protection Description
Unity Pro XLS checks at edition time and at build time that only variables from the unrestricted memory area are used as input to the Safety MOVE function blocks. In addition, Unity Pro XLS provides a cross-reference feature to search for the variable usage, enabling you to check the rule easily.
WARNING
RISK OF PROCESSING INCORRECT DATA
Make sure that the data you move to the Safety memory area are correct data. Data transferred to the Safety memory area using the Safety MOVE function blocks are not automatically correct.
Failure to follow these instructions can result in death, serious injury, or equipment damage.
To help ensure that data are transferred accurately, you can write the data to 2 different variables and then compare them.
106
33003879 10/2017
