Allen-Bradley · PLC-3 Memory
Allen-Bradley 1775-MED PLC-3 128K Memory Module
128K-word PLC-3 memory for the largest listed standard application capacity in this module group.
Product Overview
At 128K words, the 1775-MED supplies 131,072 words for large PLC-3 application and data-table requirements.
The expanded capacity of 1775-MED supports complex program structures, but scan performance and I/O behavior still depend on the processor, logic workload and complete system configuration.
A maintenance replacement must preserve the saved memory image and match the PLC-3 processor chassis, because capacity alone does not establish hardware or revision compatibility.
Technical Data
| Technical Item | 1775-MED |
|---|---|
| Brand | Allen-Bradley |
| Product Type | PLC-3 Memory Module |
| Brand Country | United States |
| Controller Family | PLC-3 |
| Memory Capacity | 128K words |
| Exact Word Count | 131,072 words |
| Compatible Chassis Family | 1775-A1 / 1775-A2 / 1775-A3 |
| Smaller Family Options | 1775-ME4 / 1775-ME8 / 1775-MEA |
| System Requirement | Compatible PLC-3 processor configuration |
128K Memory Capacity
Program scale
The 131,072-word resource accommodates a larger combined logic and data requirement than ME4, ME8 or MEA.
Data organization
Structured tables and I/O images still share the module with executable instructions.
Performance review
A larger stored program should be evaluated for scan and process-response effects on the installed processor.
Large-System Data Organization
For 1775-MED, large-system data organization must be reviewed with the installed controller hardware and saved application rather than treated as an isolated catalog-number change.
- Keep a verified offline copy of the complete image.
- Record capacity use and free-word margin.
- Validate memory, I/O and communications after restoration.
Practical Questions
How many words are available in 1775-MED?
The module is rated at 128K, equal to 131,072 words. The controller uses that capacity for both program and data storage.
Does installing 1775-MED automatically improve PLC-3 scan speed?
No; it increases memory capacity rather than processor execution speed. A larger program can increase scan time, so timing should be reviewed after application growth.
What backup practice is appropriate for 1775-MED?
Maintain a verified copy of the complete application and document the data-table layout and free-memory margin. Large legacy applications are difficult to reconstruct from partial records.
Can 1775-MED replace 1775-MEA without system checks?
The larger 128K capacity does not by itself prove compatibility. Confirm the processor, chassis, revision and restored addressing before approving the change.
Why should data-table boundaries be reviewed on 1775-MED?
Large capacity can encourage scattered allocations that are hard to maintain. A documented map reduces addressing mistakes and helps future engineers understand how the controller uses memory.
What proves a 1775-MED replacement is ready for production?
The processor must recognize the full memory image without diagnostics, and I/O, communications and timing-sensitive logic must pass controlled tests. Only then should automatic process control be restored.
Quotation Accuracy
Moore Automation
Complete product codes lead to better matches
Moore Automation uses the full requested identity to distinguish capacity, revision and system-role differences across legacy automation products. Shortened numbers are not treated as sufficient when several variants share a family prefix.
The commercial response is built around the confirmed catalog, quantity and delivery requirement, with questions resolved before order placement.
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