Siemens 6ES5581-0HB11 Memory Extension

Technical Specifications and Module Design

This memory extension adds additional storage capacity to Siemens SIMATIC S5 PLCs. The Siemens 6ES5581-0HB11 expands user program and data memory for complex applications. You can install this module into any standard S5-135U or S5-155U rack slot. Its compact design fits alongside existing CPU and I/O modules. The module weighs approximately 0.38 kilograms. Its dimensions measure 25 cm in height, 5 cm in width, and 21 cm in depth.

Parameter	Specification
Brand	Siemens
Model	6ES5581-0HB11
Category	Memory Extension / RAM Expansion Module
Weight	0.38 kg
Height	25 cm
Width	5 cm (single slot)
Depth	21 cm
Memory Type	CMOS RAM (battery-backed)
Additional Capacity	64 KB
Program Steps	Approximately 32,000 additional statements
Data Words	8,192 additional words
Access Time	150 nanoseconds
Battery Type	Lithium 3.6V (replaceable)
Battery Life	5 years typical
Data Retention	Retains all data during power loss
Backplane Interface	64-pin edge connector
Power Consumption	1.5 Watts maximum
Energy Storage	Lithium battery for RAM backup
Component Count	Single PCB with RAM chips, battery holder, and logic circuits

Memory Expansion and Addressing

The module adds contiguous memory space to the existing CPU memory. The CPU automatically recognizes the additional memory at power-up. The Siemens 6ES5581-0HB11 supports both program code and data table storage. You can mix this extension with other memory modules in the same rack. The module uses CMOS RAM technology for fast read and write access. A green LED indicates when the module has power and operates normally. The memory extension does not consume any I/O addresses.

Battery Backup and Data Retention

The onboard lithium battery preserves all memory contents during power outages. The battery automatically switches in when the backplane voltage drops. The Siemens 6ES5581-0HB11 includes a low-battery detection circuit. A red LED illuminates when the battery voltage falls below 2.8V. You should replace the battery within 30 days after this warning appears. Replacing the battery with system power ON preserves the memory contents. The module retains all data for at least five years with a fresh battery.

Installation and Operational Guidelines

You must insert this module into a slot adjacent to the CPU or existing memory. The backplane supplies 5V DC power to the module automatically. The Siemens 6ES5581-0HB11 draws approximately 300 mA from the 5V supply rail. You must insert the battery with the correct polarity before operation. Reversing the battery will damage the module permanently. The module requires no configuration or addressing for normal operation. You should backup your program before replacing the battery. The module will lose all data if you remove the battery with power OFF.