Siemens 6ES5948-3UR21 | Central Processing Unit

The Siemens 6ES5948-3UR21 serves as the main processor for the S5-115U PLC. This CPU executes your control program and manages all I/O operations. It fits directly into the central rack of a SIMATIC S5 system.

Technical specifications of Siemens 6ES5948-3UR21

Parameter	Specification
Brand	Siemens
Model	Siemens 6ES5948-3UR21
Product Family	SIMATIC S5
Sub-Family	S5-115U
Category	Central Processing Unit (CPU)
Memory Type	RAM with battery backup
Memory Capacity	16 KB user program
Processing Speed	1.6 ms per 1K binary operations
Power Supply	24V DC external
Current Consumption	300 mA typical
Integrated Interfaces	1 x RS-485 (15-pin D-sub), 1 x programming port
Number of Components	1 main PCB, 1 battery holder, 4 status LEDs
Energy Storage	1 x lithium battery (for RAM retention)
Battery Type	3.6V lithium (Siemens order code 6ES5980-0AA11)
Battery Life	Approximately 1 year typical
Dimensions (L x W x H)	Approx. 25 cm x 12 cm x 5 cm
Weight	Approx. 0.5 kg
Operating Temperature	0°C to 60°C

Detailed Technical Analysis of Siemens 6ES5948-3UR21

The Siemens 6ES5948-3UR21 processes 1K binary operations in just 1.6 milliseconds. This speed handles most mid-sized automation tasks comfortably. The unit stores your user program in battery-backed RAM. Therefore, you need a functioning lithium battery to retain data during power loss.

Now let us examine its physical construction. The Siemens 6ES5948-3UR21 contains one main circuit board inside a metal housing. It features four status LEDs on the front panel. These indicators show RUN, STOP, BATTERY, and BUS ERROR conditions. The CPU weighs approximately 0.5 kilograms.

The processor includes two built-in communication ports. One RS-485 port connects to remote I/O racks or other CPUs. The second port serves as a dedicated programming interface. You can connect a programmer or operator panel to this second port directly.

Energy Storage and Battery Management

The Siemens 6ES5948-3UR21 relies on a single 3.6V lithium battery. This battery preserves your program and system parameters when you turn off the PLC. A typical battery lasts about one year in normal operation. Replace the battery annually to prevent program loss.

The CPU warns you when the battery voltage drops too low. The BATTERY LED will flash or remain steady. You can change the battery while the PLC remains powered on. This procedure prevents any loss of your user program.

Installation and Compatibility

You mount the Siemens 6ES5948-3UR21 into the leftmost slot of an S5-115U rack. The CPU requires a 24V DC external power supply. Connect this supply to the dedicated power terminals on the module. The unit draws approximately 300 milliamps under normal load.

Summary of Siemens 6ES5948-3UR21 Features

To conclude, the Siemens 6ES5948-3UR21 delivers 16KB of battery-backed program memory. It weighs 0.5 kilograms and includes two integrated communication ports. Choose this CPU to keep your S5-115U system running reliably.