Siemens 6ES5948-3UR12 Central Processing Unit

The Siemens 6ES5948-3UR12 Central Processing Unit serves as the main processor for SIMATIC S5-115U systems. This CPU executes user logic and manages all I/O operations. You will find it in medium to large-scale automation applications. It supports up to 2,048 digital and 256 analog I/O points. Therefore, this unit suits complex machinery and process control tasks.

The Siemens 6ES5948-3UR12 Central Processing Unit measures 230 mm in height and 48 mm in width. Its depth reaches 180 mm for standard rack mounting. The unit weighs approximately 0.72 kilograms. It contains one 16-bit processor and 48 KB of user memory. Two serial ports provide programming and communication interfaces. Additionally, you get eight status LEDs for system diagnostics.

Key Technical Specifications

Parameter	Value
Manufacturer	Siemens AG
Model	6ES5948-3UR12
Product Type	Central Processing Unit
Processor	16-bit @ 20 MHz
User Memory	48 KB RAM (battery-backed)
Memory Type	RAM + EPROM (onboard)
Scan Time	1.5 ms per 1K logic
I/O Capacity	2,048 digital, 256 analog
Serial Ports	2 (TTY and RS-232)
Programming Port	15-pin D-sub (TTY)
Height	230 mm
Width	48 mm
Depth	180 mm
Weight	0.72 kg
Status LEDs	8 (PWR, RUN, STOP, BATT)
Energy Storage	≈ 350 µF (capacitive)
Power Consumption	400 mA @ 5 VDC
Backup Battery	Lithium (memory retention)
Operating Temperature	0°C to +60°C
Mounting Method	S5-115U rack

Internal Architecture and Energy Storage

The Siemens 6ES5948-3UR12 Central Processing Unit stores moderate energy in its power filter. Electrolytic capacitors hold approximately 350 microfarads total capacitance. A 16-bit processor runs user logic and operating system tasks. This processor executes 1K of logic in just 1.5 milliseconds. Forty-eight KB of battery-backed RAM stores user programs and data. A lithium battery maintains memory during power-down for up to 2 years. Two serial ports support programming, printer, and point-to-point communication. Eight LEDs show power, run, stop, battery, and error status clearly. A green RUN LED lights up when the CPU executes logic normally.

Connection Interfaces and Wiring Details

You will find a 15-pin D-sub programming port on the front panel. Connect a programming device to this port for software uploads. The Siemens 6ES5948-3UR12 Central Processing Unit also includes a 25-pin D-sub RS-232 port. Use this second port for connecting printers or operator panels. The CPU features a three-position keyswitch for mode selection. Eight LEDs indicate power, run, stop, battery, and internal fault conditions. A red BATT LED lights up when the lithium battery voltage drops too low.

Configuration and Installation Steps

You slide this CPU into the leftmost slot of the S5-115U rack. First, align the module with the upper and lower card guides. Then, push it firmly until the backplane connector seats completely. Secure the front panel with the two retaining screws. Insert the lithium battery before powering on the system. The Siemens 6ES5948-3UR12 Central Processing Unit consumes 400 mA from the backplane supply. Use the STEP 5 software to write and download your control program. Connect the programmer to the 15-pin TTY port. Set the keyswitch to RUN after program download. Verify that the green RUN LED remains steady after startup. Monitor the BATT LED regularly and replace the battery when indicated.