16 Rockwell Automation Publication 1756-UM022D-EN-P - May 2017
Chapter 1   System Overview
Select System Hardware
The GuardLogix system supports SIL 3 and PLe safety applications. The 
GuardLogix controller is composed of a primary controller and a safety partner 
that function together in a 1oo2 architecture. 
Table 4 lists catalog numbers for 
primary controllers and safety partners. 
The safety partner must be installed in the slot immediately to the right of the 
primary controller. The firmware major and minor revisions of the primary 
controller and safety partner must match exactly to establish the control 
partnership that is required for safety applications.
Primary Controller
The primary controller is the processor that performs standard and safety 
functions and communicates with the safety partner for safety-related 
functions in the GuardLogix control system. Standard functions include the 
following:
• I/O control
•Logic
•Timing
• Counting
• Report generation
• Communication
• Arithmetic computations
• Data file manipulation
The primary controller consists of a central processor, I/O interface, and 
memory.
Table 4 - Primary Controller and Corresponding Safety Partner Catalog Numbers
Primary Controller Safety Partner
1756-L71S, 1756-L72S, 1756-L73S 1756-L7SP
1756-L73SXT 1756-L7SPXT
Table 5 - Memory Capacity
Cat. No.
User Memory (RAM capacity)
Standard Tasks and Components Safety Task and Components
1756-L71S 2 MB 1 MB
1756-L72S 4 MB 2 MB
1756-L73S,1756-L73SXT 8 MB 4 MB