6ES5103-8MA03 SIMATIC S5-100U

SKU: 6ES5103-8MA03 Category: PLC

Description
Additional information

The Siemens SIMATIC S5-100U is a compact programmable logic controller belonging to the classic SIMATIC S5 series, one of Siemens' foundational PLC product families. The part number 6ES5103-8MA03 identifies a CPU module within the S5-100U family, designed for small to medium automation tasks requiring reliable sequential and combinatorial control. This module operates as the central processing unit of the S5-100U system, executing the user program stored in its memory and coordinating communication with connected I/O modules.

The 6ES5103-8MA03 CPU features an 8-bit processor architecture typical of the S5-100U series, with onboard program memory and support for EPROM or RAM memory submodules for user program storage. It communicates with expansion modules via the S5 backplane bus and supports the STEP 5 programming language, including function block diagram (FBD), ladder diagram (LAD), and statement list (STL) programming methods. The module includes a mode selector switch for RUN, STOP, and RUN-P modes, a battery-backed RAM for retentive data storage, and diagnostic LEDs for status indication including POWER, RUN, and STOP states.

The SIMATIC S5-100U CPU 6ES5103-8MA03 is widely deployed in manufacturing automation, machine tool control, conveyor systems, and process control applications across industries such as automotive, food and beverage, chemical processing, and general factory automation. Its compact form factor and modular expandability make it suitable for standalone machine control as well as integration into larger distributed control architectures. Although the S5 series has been superseded by the SIMATIC S7 family, many installations continue to operate with S5 hardware, making refurbished and replacement units such as this one highly sought after for maintenance and spare parts purposes.

Technical Specifications

Series/Product Family	SIMATIC S5-100U
Module Type	CPU Module
Programming Language	STEP 5 (LAD, FBD, STL)
Input/Operating Voltage	24 V DC
Memory Type	Battery-backed RAM, EPROM submodule support
Bus System Compatibility	SIMATIC S5 backplane bus
Operating Temperature	0 °C to +60 °C
Storage Temperature	-40 °C to +70 °C
Relative Humidity	15 % to 95 % (non-condensing)
Mounting	DIN rail or panel mounting
Certifications	CE, UL
Operating Modes	RUN, STOP, RUN-P

Common System Event Codes

STOP (Red LED): CPU has entered STOP mode due to a programming error, hardware fault, or manual mode switch activation.
Check the mode selector switch position, review the STEP 5 diagnostic buffer for fault details, and verify the user program for errors before restarting.
BASP (Bus Error): A bus fault has been detected on the S5 backplane bus, indicating a communication failure between the CPU and one or more I/O modules.
Inspect all module connections and seating on the backplane, check for damaged modules, and verify that all module addresses are correctly configured.
Memory Error: The CPU has detected an error in program memory, typically caused by a corrupted EPROM submodule or failed battery-backed RAM.
Replace the EPROM submodule or check the backup battery voltage. Reload the user program if RAM content has been lost.
Battery Fault: The backup battery voltage is low or the battery is missing, risking loss of retentive data and program memory.
Replace the lithium backup battery with the correct type as specified in the S5-100U manual. Reload the user program after battery replacement if memory was lost.
I/O Access Error: The CPU cannot access one or more configured I/O modules, often due to a missing or faulty module.
Verify that all configured I/O modules are present and correctly seated. Check module addressing and replace any faulty modules.
Watchdog Timeout: The CPU watchdog timer has expired, indicating the user program cycle time has exceeded the configured maximum scan time.
Review the user program for infinite loops or excessively long routines. Increase the watchdog time setting if the extended cycle time is acceptable.
EPROM Checksum Error: A checksum mismatch has been detected in the EPROM program memory submodule, indicating corrupted or incorrectly programmed memory.
Re-program or replace the EPROM submodule. Verify the programming device and STEP 5 software settings match the module type.

Frequently Asked Questions

What programming software is required for the 6ES5103-8MA03?

This CPU is programmed using Siemens STEP 5 software, which runs on compatible Windows-based or older DOS-based programming devices (PGs). A suitable programming cable or adapter is required to connect the PG to the CPU's programming interface.

Is the 6ES5103-8MA03 compatible with SIMATIC S7 hardware?

No, the S5-100U CPU is not directly compatible with S7 hardware or software. Migration from S5 to S7 requires program conversion using Siemens' S5/S7 migration tools and appropriate S7 hardware.

What type of backup battery does this CPU use?

The S5-100U CPU uses a lithium backup battery to retain RAM data and the real-time clock during power loss. The battery type and replacement procedure are specified in the S5-100U hardware manual.

Can the 6ES5103-8MA03 be expanded with additional I/O modules?

Yes, the S5-100U system supports expansion with digital and analog I/O modules connected via the S5 backplane bus. The number of expansion modules is limited by the CPU's addressing capacity and the physical expansion rack configuration.

What is the supply voltage for this CPU module?

The 6ES5103-8MA03 CPU module operates on a 24 V DC supply voltage, typically provided by a dedicated S5-compatible power supply unit.

Troubleshooting

CPU remains in STOP mode after power-up

Check the mode selector switch position on the CPU front panel. Review the STEP 5 diagnostic buffer for any recorded fault events. Verify that the user program is correctly loaded in memory.

Set the mode selector to RUN or RUN-P. Clear any faults recorded in the diagnostic buffer, reload the user program from the EPROM submodule or programming device, and cycle power.

Loss of user program after power cycle

Check the backup battery voltage indicator or measure the battery voltage directly. A depleted or missing battery will cause RAM contents to be lost when power is removed.

Replace the lithium backup battery with the correct replacement type. After battery replacement, reload the user program from the EPROM submodule or programming device and verify correct operation.

No communication between programming device and CPU

Verify the programming cable connections between the PG and the CPU programming port. Check that the STEP 5 software is configured for the correct COM port and communication parameters. Ensure the CPU is in STOP or RUN-P mode, which allows programming access.

Replace or reseat the programming cable. Reconfigure the STEP 5 communication settings to match the CPU interface. If using a USB-to-serial adapter, verify driver compatibility with the STEP 5 software version.

I/O modules not responding or showing errors

Inspect the physical seating of all I/O modules on the backplane. Check module address settings using the address switches on each module. Review the STEP 5 hardware configuration for address conflicts.

Reseat all I/O modules firmly in their slots. Correct any address switch settings to match the STEP 5 hardware configuration. Replace any modules that show visible damage or fail diagnostic checks.

CPU overheating or thermal shutdown

Check the ambient temperature around the PLC installation. Verify that ventilation slots on the CPU and enclosure are not blocked. Inspect the cooling fan if fitted to the enclosure.

Ensure the installation environment is within the specified operating temperature range of 0 °C to +60 °C. Clear any obstructions from ventilation slots and improve enclosure ventilation or add forced-air cooling if necessary.

Condition	Repair, Used, Refurbished, New in box (sealed)