Description
The Siemens 6ES5377-0AA21 is a specialized EPROM (Erasable Programmable Read-Only Memory) submodule designed for the SIMATIC S5 series of programmable logic controllers. As part of the S5 377 memory family, this compact daughterboard plugs directly into compatible high-end CPUs—including the S5-115U, S5-135U, and S5-155U—providing 32KB of truly non-volatile program storage that remains intact without any battery backup .
Unlike volatile RAM modules that rely on lithium batteries to preserve data during power-downs, the Siemens 6ES5377-0AA21 leverages EPROM technology to store user programs, data blocks, and critical parameters permanently. Once programmed—using a specialized EPROM programmer or a CPU with integrated programming capability—the data is physically locked into the silicon, offering both run-only protection against accidental modification and immunity to power interruptions . For industries operating mission-critical S5 systems decades after the platform’s discontinuation, this module represents the ultimate safeguard against program loss.
Application Scenarios
In a nuclear-grade chemical processing facility, an S5-155U system controlled a multi-stage reactor sequence with interlocks calibrated to strict safety margins. When a maintenance technician inadvertently downloaded a test program that overwrote the production logic, the entire batch had to be aborted—costing over $120,000 in raw materials. The facility’s solution was to permanently burn the validated program into a fleet of Siemens 6ES5377-0AA21 modules and distribute them as “golden copies.” Now, even if the CPU’s volatile memory is corrupted, operators can simply swap in the 6ES5377-0AA21 to restore the original logic in seconds. The module’s physical write-protection ensures that only authorized personnel with the correct UV eraser and programmer can alter the code, eliminating the risk of human error or malicious tampering .
Parameters
| Main Parameters | Value / Description |
|---|---|
| Product Model | Siemens 6ES5377-0AA21 (MS 377) |
| Manufacturer | Siemens AG (SIMATIC S5 Series) |
| Product Category | EPROM Memory Submodule |
| Storage Capacity | 32 KB (user program + data area) |
| Memory Technology | EPROM (Erasable Programmable Read-Only Memory), floating-gate transistor |
| Data Retention | > 10 years (permanent, no battery required) |
| Erase Method | Ultraviolet (UV) light exposure, wavelength 253.7 nm |
| Write Method | Requires dedicated EPROM programmer or compatible CPU/interface with programming capability |
| Operating Voltage | 5 V DC (backplane-powered) |
| Power Consumption | ~0.4 W typical (low during read operations) |
| Compatible CPUs | SIMATIC S5-115U, S5-135U, S5-155U (CPU submodule slot) |
| Operating Temperature | 0°C to +60°C |
| Storage Temperature | -40°C to +70°C |
| Protection Class | IP20 (for installation in control cabinet CPU slot) |
