IC693CPU313 Memory Retention and Expansion Limits Before Replacement

A GE Fanuc IC693CPU313 replacement is not the same job as changing a plug-in Series 90-30 CPU. The CPU313 combines the processor, memory and five-slot baseplate on one assembly. A failure therefore removes both the controller and the backplane that carries its local modules.

This distinction affects backup planning, spare selection and outage time. It also explains why a modular CPU or an expansion baseplate should not be treated as a direct substitute.

What the IC693CPU313 actually contains

The GE Fanuc Series 90-30 hardware manual identifies the IC693CPU313 as a five-slot baseplate with an embedded 80188 processor running at 10 MHz. The processor and memory are soldered to the backplane. All five numbered slots remain available for Series 90-30 I/O or option modules because there is no removable CPU module occupying a slot.

The same manual limits the system to one baseplate. The CPU313 has no expansion connector and does not support expansion or remote baseplates. An IC693CHS398 expansion baseplate belongs to a modular Series 90-30 architecture; it cannot extend a CPU313 system.

Specifications that matter during replacement

Architecture	Five-slot baseplate with embedded CPU
Processor	80188 at 10 MHz
Power-supply load	430 mA at +5 V DC
Typical scan rate	0.6 ms per 1K of Boolean logic
User program memory	12 KB maximum; 6 KB before firmware Release 7
Register memory	1,024 words of %R memory
Analog references	64 words of %AI and 32 words of %AQ
Discrete I/O limit	160 points maximum, combined inputs and outputs
Built-in serial protocol	SNP/SNP-X slave through the power-supply connector
Time-of-day clock	Not provided

These values are useful for checking a candidate spare, but they do not prove interchangeability by themselves. The fitted power supply, firmware release, optional memory device and installed modules still need to be recorded from the working system.

Memory retention is the first outage risk

The CPU313 stores its application in RAM. Its long-term backup battery is located in the Series 90-30 power supply, not on the CPU baseplate. The baseplate also has a supercapacitor that can retain memory during a power-supply change. GE documents a minimum hold-up of one hour after the baseplate has been powered long enough to charge it.

That capacitor is an emergency bridge, not a backup method. Its charge state, age and actual retention time may be unknown. Before removing power, archive the application, configuration and reference tables with the correct Series 90-30 programming tools. If an EPROM or EEPROM is installed, record its type and whether the operating program is being loaded from it.

Firmware matters as well. GE lists 12 KB as the maximum user program memory for CPU313 units at Release 7 and later, but only 6 KB for earlier firmware. A program that fits a later spare may not fit an older unit.

The programming port is part of the power-supply assembly

The built-in serial connection is physically presented through the power-supply connector. It operates as an SNP or SNP-X slave. This matters when a replacement baseplate is tested on the bench: communication depends on the installed power supply and the correct cable, not only on the CPU baseplate.

The built-in port is not a general Ethernet interface, and the CPU313 does not provide an embedded Ethernet port. If the original rack uses an optional communication module, preserve that module, its slot and its configuration as separate migration items.

Why modular Series 90-30 parts are not drop-in replacements

A modular unit such as the IC693CPU360 single-slot CPU separates the processor from the baseplate. The CPU313 does not. Moving to a modular CPU therefore becomes a conversion project: the new baseplate, CPU, power supply, module layout, memory map and communication path must all be validated.

Editorial analysis: for a short maintenance outage, an exact IC693CPU313 spare normally reduces the number of variables. A modular conversion may offer a different service strategy, but it should be engineered and tested as a system change rather than described as a direct replacement.

Pre-removal checklist

1. Save the controller program, hardware configuration and reference tables.
2. Record the CPU313 firmware revision and the power-supply catalog number.
3. Photograph the five slot positions, module catalog numbers and terminal wiring.
4. Record any EPROM or EEPROM option and the current memory source.
5. Confirm the programming cable and SNP/SNP-X communication settings.
6. Check the spare for the exact IC693CPU313 catalog number and compatible firmware capacity.
7. After installation, verify program checksum, I/O mapping, serial communication and every safety-related interlock before returning the machine to service.

Procurement boundary

The IC693CPU313 product page should be used to confirm the catalog identity and available unit. It cannot establish the firmware release or optional memory fitted to an existing controller. Those details must come from the installed hardware and the saved project.

For related legacy hardware, see the GE Series 90-30 and 90-70 collection. Do not infer compatibility from the shared Series 90-30 name alone.

Source documents

• GE Fanuc Automation, Series 90-30 Programmable Controller Installation and Hardware Manual, GFK-0356P, October 1999.
• PLC ProTech archived IC693CPU313 product document.