Siemens 6ES5905-3RB21 | SIMATIC S5 Memory Submodule

The Siemens 6ES5905-3RB21 offers additional storage for your PLC system. This memory submodule belongs to the SIMATIC S5 controller family. It plugs directly into compatible CPU or memory expansion units. You can use it to store user programs and system parameters securely.

Key Technical Specifications

Below you will find the accurate technical parameters for the Siemens 6ES5905-3RB21.

Parameter	Specification
Product Type	Memory Submodule
Series	SIMATIC S5
Memory Type	EEPROM
Storage Capacity	8 KB
Interface	Direct slot connection
Operating Voltage	5 V DC (from backplane)
Data Retention	Non-volatile (no battery)
Write Cycles	10,000 minimum
Manufacturer	Siemens

The submodule measures 40 mm in width and 50 mm in height. Its total depth reaches 10 mm. The Siemens 6ES5905-3RB21 weighs approximately 20 grams. This unit contains a single EEPROM chip on a compact PCB. Energy storage does not apply to this non-volatile component.

You will find a polarization notch on the connector edge. This feature prevents incorrect insertion into the socket. Consequently, you cannot damage the module or the host device. The EEPROM retains all data for over ten years without power.

Installation and System Integration

You can insert the Siemens 6ES5905-3RB21 into any compatible S5 slot. The module draws operating power directly from the backplane bus. Therefore, you do not need any external battery or wiring. The CPU recognizes this submodule automatically during power-up.