Omron C500-ASC02 ASCII/BASIC Unit for SYSMAC C500 PLCs

The Omron C500-ASC02 is an intelligent I/O module for the SYSMAC C500 programmable logic controller series. Acting as a coprocessor for the main CPU, this unit runs application-specific programs written in the BASIC programming language and handles high-level serial communication tasks. It is the primary solution for adding custom communication protocols, data logging, or mathematical calculations to legacy Omron C-Series systems.

Key Specifications

• Model: C500-ASC02 (ASCII/BASIC Unit)

• Host Compatibility: SYSMAC C500, C200H, C1000H PLC systems

• Processor: Dedicated CPU (runs independently of main PLC scan)

• Program Language: BASIC (standard syntax, arithmetic, string handling)

• Communication Ports: 1 x RS-232C (configurable as Host Link or No-Protocol)

• Memory: Battery-backed RAM for user programs (non-volatile)

• Data Exchange: Via PLC user program (from BASIC to ladder using MOV/PRV instructions)

• Applications: Modbus master/slave, printer output, barcode reader interface, custom serial protocol

• Power Supply: Supplied via PLC backplane

• Status Indicators: RUN, ERR, COM indicators

Communication and Protocol Handling

The C500-ASC02 is primarily used to interface the PLC with devices that use ASCII (text-based) communication protocols, such as printers, weighing scales, and barcode scanners. A typical application involves writing a BASIC program that polls a RS-232 barcode scanner, parses the incoming string, extracts the numeric code, and moves that value into a specific word in the PLC's memory (e.g., DM2000). This frees the main PLC processor from the heavy task of parsing variable-length serial strings.

Advanced Protocol Capabilities

One of the most powerful applications for the ASC02 is to serve as a Modbus protocol master. When loaded with the appropriate software (e.g., Modbus Master utility software), the ASC02 allows the Omron C-Series PLC to communicate seamlessly over RS‑485/RS‑232 with a variety of Modbus RTU slave devices, such as AC drives, MODBUS remote I/O, and power meters, allowing legacy C-Series PLCs to interface with modern smart sensors.

Memory and Data Exchange with the PLC

The unit executes its user program in parallel to the PLC's ladder scan. A configuration utility allows the mapping of a block of DM (Data Memory) or EM (Extended Memory) words from the PLC to the internal variables of the BASIC program. The PLC uses standard MOV(21) instructions to write to these memory addresses, which the BASIC program can then read and process. Conversely, the BASIC program writes output data to these mapped registers, making them available to the ladder logic.

Integration with C200H / C500 Systems

While the model number begins with C500, the ASC02 is also fully compatible with the C200H CPU mounting on a C200H expansion rack. It occupies one unit slot and is recognized by the I/O table as a special I/O unit.

Conclusion

The Omron C500-ASC02 ASCII/BASIC Unit is a versatile tool for bridging the gap between legacy C-Series controller hardware and continuously evolving field devices. Its ability to act as a communication gateway (e.g., Modbus master) breathes new life into older PLC systems, making the C500-ASC02 an essential power tool for system integrators and maintenance electricians when interfacing older stations with modern peripherals.