Siemens 6ES5374-1FH21 Memory Card

Technical Specifications and Card Design

This memory card stores user programs and system parameters for SIMATIC S5 PLCs. The Siemens 6ES5374-1FH21 provides non-volatile storage without continuous battery backup. You can install this card directly into the CPU or expansion rack. Its compact cartridge design allows quick replacement during maintenance. The card weighs approximately 0.11 kilograms. Its dimensions measure 12 cm in height, 8 cm in width, and 2 cm in depth.

Parameter	Specification
Brand	Siemens
Model	6ES5374-1FH21
Category	Memory Card / EPROM Program Storage Cartridge
Weight	0.11 kg
Height	12 cm
Width	8 cm
Depth	2 cm
Memory Type	EPROM (Erasable Programmable Read-Only Memory)
Storage Capacity	64 KB (512 Kbits)
Program Steps	Approximately 32,000 statements
Data Retention	Over 10 years without power
Number of Memory Chips	4 x 16 KB EPROMs
Erasure Method	UV light (through quartz window)
Interface Type	64-pin edge connector
Access Time	250 nanoseconds
Operating Temperature	0°C to 60°C
Energy Storage	None (no battery required)
Component Count	4 EPROMs, 1 PCB, 1 plastic housing, 1 quartz window

EPROM Technology and Data Retention

The card uses UV-erasable EPROM technology for permanent program storage. A quartz window on top exposes the memory chips for erasure. You can erase the contents with 15 minutes of strong UV light exposure. The Siemens 6ES5374-1FH21 retains all data for over a decade without power. Consequently, you never need a backup battery for this memory card. The plastic housing protects the quartz window from accidental light exposure. A protective label covers the window during normal operation.

Compatibility and System Integration

You insert this memory card into any S5 CPU or expansion rack slot. The 64-pin edge connector matches the standard S5 memory interface perfectly. The CPU automatically loads program data from this card at power-up. You can also use the card as a read-only program backup device. The Siemens 6ES5374-1FH21 works with S5-115U, S5-135U, and S5-155U systems. It cannot write data during normal PLC operation. Therefore, you need a separate programmer to burn new EPROMs.

Installation and Handling Guidelines

You must ground yourself before handling this EPROM memory card. Static discharge will destroy the sensitive memory cells instantly. The quartz window requires protection from direct sunlight and fluorescent light. Ordinary room lighting will not affect the stored data significantly. You should cover the window with the provided label after programming. The card draws no power from the PLC backplane during operation. It only supplies stored program data when the CPU requests it.