OMRON C500-LK007 (3G2A5-LK007) Host Link Unit for C500 Series PLCs

The OMRON C500-LK007 (also known as 3G2A5-LK007) is a Host Link communication unit designed for the C500 series programmable logic controllers. It provides an RS-232C serial interface that allows the PLC to communicate with a host computer, programming console, or HMI using the SYSMAC WAY protocol. This unit is essential for programming, monitoring, and data exchange in legacy OMRON C500 systems. It supports one-to-one connections as well as one-to-N (multidrop) networks when used with appropriate line drivers.

Technical Specifications

The unit features a 9-pin D-sub connector (female) for RS-232C communication. Baud rates are selectable via DIP switches: 1200, 2400, 4800, 9600, and 19200 bps. Communication parameters: data bits (7 or 8), parity (even, odd, none), stop bits (1 or 2). The unit supports the Host Link (SYSMAC WAY) protocol, which allows a host computer to read/write PLC memory areas (IR, SR, HR, AR, LR, DM). The maximum cable length is 15 meters. Power is supplied from the PLC backplane (5 VDC, 150 mA).

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Compatibility and Installation

The C500-LK007 is designed for the C500 CPU rack (C500-BC series backplanes). It occupies one slot and can be installed in any I/O slot except the first (CPU slot). It is compatible with C500-CPU11, CPU31, CPU61, and CPU63 processors. The unit requires no additional configuration software; all settings are made via the DIP switches on its front panel. The unit number (host link node address) is set using a rotary switch (0-31). When multiple units are used in the same rack, each must have a unique unit number.

Host Link Protocol Overview

The SYSMAC WAY protocol used by the C500-LK007 is a command-response protocol. A host computer sends a command frame (e.g., “@00RR0001” to read 1 word from DM0001), and the PLC responds with a data frame. Commands include reading/writing bits, reading/writing words, forcing I/O, setting/clearing modes (run/monitor/program), and reading the PLC status. The unit automatically handles framing, error checking (FCS sum), and retries. This protocol is still supported by many SCADA systems and OMRON programming software (SYSMAC-CPT, SYSWIN).

Connecting to a Host Computer or HMI

To connect the C500-LK007 to a modern PC, a USB-to-RS232 converter (with FTDI chipset) is recommended. Use a straight-through serial cable (pin 2-2, 3-3, 5-5) with a female-to-female adapter if needed. For connection to an OMRON HMI (e.g., NT series), the cable pinout may require a crossed connection (2-3, 3-2, 5-5). The unit supports both DTE and DCE configurations via an internal jumper (factory set as DTE). The host computer must be configured with the same baud rate and parity as the unit.

Environmental Specifications

Operating temperature: 0°C to 55°C, storage -20°C to 75°C. Humidity: 35% to 85% non-condensing. The unit is rated IP20 and is designed for installation inside a control cabinet. It meets CE and UL standards (for legacy certifications). Dimensions: 250mm (H) x 50mm (W) x 150mm (D) (C500 module size). Weight: 0.4 kg.

Typical Applications

The C500-LK007 is used in legacy systems to: upload/download programs from a PC running SYSMAC-CPT, connect to a SCADA system for data logging, interface with a serial printer for alarm reporting, or link to an OMRON NT-series HMI for operator interface. It is also used as a gateway to extract data from aging C500 PLCs before system migration. In many factories, this unit remains in service due to the reliability of C500 hardware.

Maintenance and Troubleshooting

Common issues include: no communication due to incorrect baud rate or unit number, missing termination resistors (not required for RS-232C), or faulty cable. The LEDs indicate power (PWR) and data transmission (SD/RD). If the unit fails, it may be repaired by replacing the serial driver chip (MAX232). However, because the C500 series is discontinued, replacement units are available from aftermarket suppliers. OMRON no longer provides technical support for the C500 series, but manuals are available from online archives. The C500-LK007 is also known as 3G2A5-LK007 in older catalogs.

Ordering Information

Original part numbers: C500-LK007 (Japanese version) and 3G2A5-LK007 (export version). The unit does not include a serial cable; order a 9-pin D-sub straight cable separately. For long-distance communication, an RS-232C to RS-422 converter (e.g., OMRON C500-LK009) can be used. This product is obsolete but documented here for legacy system support.