Siemens 6ES5944-7UB21 Central Processing Unit

This central processing unit executes complex automation tasks for SIMATIC S5 systems. It handles large user programs with fast scan times. You can pair this CPU with up to 32 I/O modules.

Technical Specifications

Parameter	Details
Brand	Siemens
Model	Siemens 6ES5944-7UB21
Category	Central Processing Unit (SIMATIC S5 Series)
Dimensions (H x W x D)	250 mm x 85 mm x 210 mm
Weight	1.60 kg
Processor Type	16-bit microprocessor
Program Memory	32 KB RAM (battery-backed)
Load Memory	32 KB EPROM or EEPROM
Data Memory	4 KB internal flags and timers
Processing Speed	1.5 ms per 1K of bit logic
Number of Internal Components	1 CPU + 2 memory submodules + 1 real-time clock
Interface Type	Backplane bus + 1x TTY + 1x RS-232 (optional)
Built-in I/O	None (requires external S5 modules)
Power Supply	5 V DC from backplane only
Current Draw (5V)	800 mA typical
Built-in Energy Storage	4700 µF capacitor + lithium battery socket
Battery Type	3.6 V lithium (not included)
Data Retention (with battery)	Approximately 100 days
Real-Time Clock	Yes (with battery backup)
Status Indicators	6 LEDs (RUN, STOP, BATT, BUS, INT, RTC)
Operating Temperature	0°C to 60°C

Detailed Feature Overview

This central unit provides 32 KB of user program memory. It processes 1K of bit logic in just 1.5 milliseconds. Consequently, it suits high-speed packaging or assembly machines.

A 4700 µF capacitor offers substantial buffering during power dips. With an optional lithium battery, data retention extends up to 100 days. The real-time clock keeps accurate timestamps for event logging.

You will find a backplane bus connector at the rear of this CPU. This bus communicates with up to 32 S5 I/O modules simultaneously. An optional RS-232 port allows connection to modern programming devices.

Installation and Compatibility

Siemens 6ES5944-7UB21 occupies the first slot of an S5 rack. Use STEP 5 software to upload programs via the TTY port. Always insert a memory submodule before applying backplane power.