CJ2M vs CJ3M Comparison Table (CPU Unit Replacement)

This table summarizes the differences in specifications between the OMRON CJ2M CPU unit (CJ2M-CPU□□) and its replacement, the CJ3M CPU unit (CJ3M-CPU□□). Yellow cells are items whose specifications changed from the CJ2M. For the meaning of the symbols, see the legend at the end of the page.

Key specifications

Program capacity (max.)60k steps→100k steps
Number of EM banks (max.)4 banks→10 banks
Number of network variables (tags)2,000→10,000
BatteryBuilt in→Sold separately
Battery-free backupNone→Backed up in non-volatile memory
Built-in capacitor backup time5 minutes→10 days (clock only)
USB portType-B→Type-C
Memory cardCF card→SD card
Built-in EtherNet/IP tag data linksRestrictions such as link size removed; equivalent to the EIP unit
Built-in EtherNet/IP communication servicesSupports socket services and Modbus server/client

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Main Specification Changes in CPU Functions

Item	CJ2M CJ2M-CPU□□	CJ3M CJ3M-CPU□□	Remarks
Max. I/O points	2,560 points	5,120 points
Max. number of expansion racks	3 racks	7 racks
Max. number of units	40 units Basic I/O: 40 / Special I/O: 40 CPU Bus: CPU1□ 16, CPU3□ 15	80 units Basic I/O: 80 / Special I/O: 80 CPU Bus: CPU1□ 16, CPU3□ 15
Number of CJ1W-EIP21S/EIP21 units mountable	CPU1□: 2 CPU3□: 2	CPU1□: 8 CPU3□: 7
Program capacity	CPU□1: 5k steps CPU□2: 10k steps CPU□3: 20k steps CPU□4: 30k steps CPU□5: 60k steps	CPU□1: 5k steps CPU□2: 10k steps CPU□3: 20k steps CPU□4: 50k steps CPU□5: 100k steps	Increased for □4/□5 only
FB program area	20k steps	40k steps
Number of EM banks	CPU1□/2□/3□: 1 bank CPU4□/5□: 4 banks	CPU1□/2□/3□: 1 bank CPU4□/5□: 10 banks
Max. FB definitions / max. instances	CPU1□/2□/3□：256／256 CPU4□/5□：2048／2048	All models 2048 / 2048
Number of registered network variables (tags)	Max. 2,000	Max. 10,000
Data trace memory capacity	8,000 words	220,000 words
Battery-free I/O memory backup	No (I/O memory backed up by battery at power OFF)	Yes (backed up in non-volatile memory, no battery needed)
Battery	Built in at shipment (CJ1W-BAT01)	Not built in at shipment Sold separately (CJ1W-BAT01)	Must be mounted to use the clock
Clock	Built in (same)
Built-in capacitor backup time	5 minutes (without battery) Backs up I/O memory and clock	10 days (without battery) Backs up clock only
Peripheral USB port	Type-B connector	Type-C connector
Serial port	CPU1□: RS-232C CPU3□: CP1W option board	RS-232C port (all models)	Option board slot removed on CPU3□. RS-422A/485 supported with converter units (CJ1W-CIF11 / NT-AL001)
Memory card	HMC-EF□□□	HMC-SD□□□ (SD memory card)
Power-up time (startup time of the CPU alone)	Approx. 2 s	CPU1□: approx. 2 s CPU3□: approx. 6 s
Current consumption	CPU1□：DC5V 0.5A CPU3□：DC5V 0.7A	CPU1□：DC5V 0.26A、DC24V 0.003A CPU3□：DC5V 0.91A、DC24V 0.003A	5 V consumption increased on CPU3□. Check the power supply unit capacity
Model name returned by Read CPU Unit Data (FINS 0501)	CJ2M-CPU□□	Returns "CJ2X-CPU□□"	Note that it is not "CJ3M-CPU□□". Shown as CJ3M in CX-One

Specification Changes in Built-in EtherNet/IP Functions

Comparison of CJ2M-CPU3□ → CJ3M-CPU3□ (built-in EtherNet/IP type).

Item	CJ2M CJ2M-CPU3□	CJ3M CJ3M-CPU3□	Remarks
Number of tag data link connections	32	256
Packet interval (RPI)	1 to 10,000 ms (0.5 ms units)	0.5 to 10,000 ms (0.5 ms units)
Permissible communication bandwidth per unit	3,000pps	12,000pps
Number of registrable tags	32	256
Number of tags per connection	8 (same)
Max. link data size per node	640CH	184,832CH
Max. data size per connection	640CH	722CH
Number of registrable tag sets	32	256
Max. size of one tag set	640CH	722CH
Max. number of tags refreshable per cycle	Output/send: 32 Input/receive: 32	Output/send: 256 Input/receive: 256
Data size refreshable per cycle	Output/send: 640 CH Input/receive: 640 CH	Output/send: 6,432 CH Input/receive: 6,432 CH
Explicit messages Class 3	Number of connections: 128 (same)
Explicit messages UCMM (unconnected)	Simultaneous communication: max. clients 16 Max. servers 16	Simultaneous communication: max. clients 32 Max. servers 32
CIP routing	Supported (same)
FINS/UDP, FINS/TCP	Supported (FINS/TCP max. 16 connections) (same)
Socket services	Not possible	Supported (UDP max. 8 sockets, TCP max. 8 sockets)
Modbus server	Not possible	Supported (TCP max. 8 connections, UDP supported)
Modbus client	Not possible	Supported (implemented with FBs using socket services, TCP max. 8 connections / UDP)
EtherNet/IP conformance test	CT17 (A5 compliant in the appendix table)	CT21
Ethernet interface	100BASE-TX / 10BASE-T Auto Negotiation / fixed setting	100BASE-TX / 10BASE-T Auto Negotiation / fixed setting Auto MDI/MDI-X
Carrying over FTP settings	―	Not carried over	When using FTP, set "Use FTP", the password and the port number again
Getting the IP address via BOOTP	"Get from BOOTP server"	Converted to "Get from BOOTP server (once only)"	Same behavior. However, the MAC address changes, so the BOOTP server settings must be changed

Differences in External Interfaces (Parts)

Item	CJ2M	CJ3M	Remarks
Battery	Mounted at shipment (CJ1W-BAT01)	Not mounted at shipment (sold separately: CJ1W-BAT01)
DIP switch	Layout and settings are the same		Set to the same ON/OFF states as the CJ2M. SW3/SW4/SW8 on the CJ3M have functions assigned but should be OFF
Status LEDs	RUN、ERR/ALM、INH、PRPHL、COMM、BKUP	RUN、ERR/ALM、INH、COMM、BKUP	The function of each LED is the same. No PRPHL LED
Memory card LED	BUSY、MCPWR	SD BUSY、SD PWR	Different name but same function
USB port	Type-B	Type-C
Memory card	HMC-EF□□□	HMC-SD□□□
RS-232C port (CPU1□)	Connector (D-sub 9-pin) and pin assignment are the same
Option board slot (CPU3□)	RS-232C and RS-422A/485 option boards (CP1W-CIF□□) can be mounted	No slot → RS-232C port	RS-422A/485 supported with CJ1W-CIF11 (non-isolated) or NT-AL001 (isolated)
EtherNet/IP setting switches	Unit number and node address setting (same)
EtherNet/IP LEDs	7SEG, MS, NS, COMM, 100M, 10M (same)
EtherNet/IP port	RJ45 (same)
Dimensions (H × D × W)	CPU1□: 90×75×31 mm / CPU3□: 90×75×62 mm (same)
Weight	CPU1□: 130 g max. CPU3□: 190 g max.	CPU1□: 140 g max. CPU3□: 240 g max.

Battery, I/O Memory Retention and Clock

Item	CJ2M	CJ3M	Remarks
Battery mounted at shipment	Mounted	Not mounted
PLC Setup Battery error detection (default)	Detect	Do not detect	Change to "Detect" when using a battery
I/O memory	SRAM	Non-volatile RAM
I/O memory retention at power OFF	Backed up by battery	No battery needed
Clock	Built in (same)
Built-in capacitor backup time for the clock	5 minutes	10 days (ambient temperature 40°C)	No battery needed for short power interruptions
Battery used	CJ1W-BAT01 (same)		Life 5 years (0 to 55°C)
Clock accuracy (per month)	55°C: -3.5 to +0.5 min / 25°C: -1.5 to +1.5 min / 0°C: -3 to +1 min (same)

Caution: when migrating, the meaning of the battery error detection setting is reversed When migrating by program conversion or simple backup, the ON/OFF state of "Do not detect battery error" in the PLC Setup is carried over as-is, but on the CJ3M the setting name becomes "Detect battery error", so the meaning is reversed. If you mount a battery and use the clock, turn "Detect battery error" ON on the CJ3M. If it is left as "do not detect", battery depletion will not be detected and programs that use time data may malfunction.

Setting	CJ2M "Do not detect battery error"	CJ3M "Detect battery error"
OFF	Detect battery error	Do not detect battery error
ON	Do not detect battery error	Detect battery error

Overview of How to Replace CJ2M with CJ3M

For details on replacement, refer to the Programmable Controller CJ Series Replacement Guide: From CJ2M to CJ3M, catalog number SBCA-150A (as of September 2026), and other materials. This is an excerpted overview.

Data to migrate	Method A: project file conversion (CJ2M→CJ3M CXP converter)	Method B: simple backup/restore (via memory card)
Program (including FBs)	○	○
Data types / variable tables	○	○ (variable tables, comments, program index)
PLC memory / I/O memory	○ (PLC memory)	○
PLC Setup	○	○
I/O table	○	○
Special unit settings	○ (except built-in EtherNet/IP)	○ (except built-in EtherNet/IP)
Routing tables	Read/transfer separately with CX-Integrator	○
Built-in EtherNet/IP settings	Not carried over → in the I/O table, "Save Special Unit Parameters" (.xml) for the CJ2M-EIP21, then "Load Special Unit Parameters" for the CJ3M-EIP21S	Not carried over (MS LED flashes red, 7-segment shows "Er" "H8") → migrate following the procedure in the replacement guide
Tag data link settings	Upload the entire network with Network Configurator → "Change Device" to CJ3M-CPU3□ → download the entire network (the settings of partner PLCs must also be transferred)
CJ1W-CLK□□ / CJ1W-FLN22	Read/transfer separately with CX-Integrator (data link tables) / CX-Flnet

Restrictions when migrating

The converter "CJ2M-CJ3MConverter.exe" is available from the Sysmac Studio / CX-One Utility download page. Conversion is not possible if the project contains multiple PLCs (prepare a file with only one CJ2M).
The converter only changes the model from "CJ2M" to "CJ3M". Change the CPU type (CPU□□) in CX-Programmer after conversion. From models other than CJ2M, migrate by changing the model in CX-Programmer (PLC Setup, I/O table and special unit settings are initialized).
After conversion, compiling (program check) may produce errors, so check and fix them.
Simple backup: if the program capacity of the backup is larger than the restore destination, it is not restored.
Simple backup: if the number of EM banks is smaller at the restore destination, the EM in the file is restored but force-set/reset information is not (e.g. CJ2M-CPU13 → CJ3M-CPU15). If larger, it is not restored (e.g. CJ2M-CPU15 → CJ3M-CPU13).
Simple backup: if units have been added or special unit numbers differ, it is not restored.
When using CJ1W-ETN21, if memory all clear is performed, settings cannot be transferred unless the power is cycled or the unit is restarted.

Summary of Points to Note When Replacing

Item	Description
Cycle time	Changing to the CJ3M may change the cycle time. Check the operation of programs that depend on the cycle time. To make it the same as the CJ2M, use the "Minimum cycle time" function in the PLC Setup.
Floating-point arithmetic	Real-number calculation results may differ. Check real-type calculation results thoroughly.
Battery error detection	The CJ3M defaults to "do not detect". When using the clock, mount a battery and set it to "detect" (note that the meaning of the setting is reversed when migrating).
Built-in EtherNet/IP	Neither the model conversion tool nor simple backup carries over the built-in EtherNet/IP settings. FTP settings must be set again. When using BOOTP, change the server side because the MAC address changes.
FINS 0501	The model name is returned as "CJ2X-CPU□□". Action is needed if host applications check it.
Power supply capacity	5 V current consumption of CPU3□ increases from 0.7 A to 0.91 A. Check the power supply unit capacity.
Startup time	Power-up of CPU3□ goes from approx. 2 s to approx. 6 s. Pay attention to startup timing with host devices.
Memory card	Changed from HMC-EF to HMC-SD. Migrate data by copying it on a PC (files can be used as-is).

For the procedure for migrating programs and settings, refer to OMRON's "Replacement Guide: From CJ2M to CJ3M (SBCA-150A)".

No matching items found.

Legend

	Items whose specifications changed from the CJ2M
(same)	Items with the same specifications on CJ2M and CJ3M (shown with the 2 columns merged)
□	A digit of the model number goes here (e.g. CPU1□ = CPU11 to CPU15, CPU□4 = CPU14 and CPU34)
CPU1□	Built-in RS-232C type
CPU3□	Built-in EtherNet/IP type

Sources

OMRON: Programmable Controller CJ Series Replacement Guide: From CJ2M to CJ3M, catalog number SBCA-150A (as of September 2026)
For details, refer to the CJ3 CPU Unit User's Manual Hardware (SBCA-513), the CJ2/CJ3 CPU Unit User's Manual Software (SBCA-350) and the EtherNet/IP Unit User's Manual (SBCD-342).
This page is organized based on manufacturer documents. Always check the latest manuals when actually replacing units.