How to Configure Port 3 on the IC693CPU363 for Raw ASCII Label Printer Control
Industrial automation engineers often need to connect legacy PLC hardware to modern serial peripherals. The GE Fanuc Series 90-30 IC693CPU363 CPU module supports this need through its Serial I/O protocol. This guide explains how to switch Port 3 into raw ASCII mode using COMMREQ instructions. As a result, you can drive serial label printers directly from the controller.
Understanding the IC693CPU363 Hardware Architecture
The IC693CPU363 is a single-slot CPU for the Series 90-30 platform. It runs an 80386EX processor at 25 MHz. Moreover, it provides 240 KB of user memory for ladder logic. This module includes three built-in communication ports. Port 1 uses RS-232, while Port 2 offers RS-485 for multi-drop networks. Port 3 serves as the primary serial interface for peripheral devices. In addition, the CPU handles up to 2,048 discrete inputs and 2,048 discrete outputs. Its typical scan rate is 0.22 milliseconds per 1K of Boolean logic.
Comparing Serial Protocols on the CPU363 Platform
By default, Ports 1 and 2 support SNP and SNPX master/slave protocols. The CPU also supports RTU slave operation natively. However, raw ASCII communication requires a different approach. Serial I/O protocol, formerly Custom Protocol, enables character-level control. This protocol applies specifically to the IC693CPU363. Engineers must load COMMREQ instructions into ladder logic to activate Serial I/O mode. Consequently, the CPU can transmit raw character strings to external devices. This capability proves essential for label printers using proprietary command sets.
Configuring Port 3 Through COMMREQ Instructions
The configuration process begins with the COMMREQ function block. Engineers place this instruction into the ladder program for the target port. The command block must specify the correct port number in its header. Specifically, the Initialize Port command (4300) sets communication parameters. The data block defines baud rate values for the port. Typical label printers operate at 9600 or 19200 bps. Additionally, the data block specifies data bits and parity settings. Eight data bits with no parity represent a common configuration. The block also sets one or two stop bits as required. Moreover, engineers must define input and output buffer sizes. The Set Up Input Buffer command allocates memory for received data. The Write Bytes function (4401) handles outgoing transmissions.
Practical Implementation for Label Printer Control
A single Write Bytes call transmits up to 250 characters. The data resides in %R register memory locations. Characters must remain unchanged until the operation completes. A typical label printer receives ASCII command strings from the CPU. The Write Bytes function sends these strings through Port 3. The printer interprets the commands and produces labels accordingly. For instance, engineers load command characters into consecutive %R registers. The COMMREQ data block references the starting register address. The function transmits the specified byte count to the printer. Timeout values protect against communication failures. A 30-second timeout represents a reasonable default. However, a zero timeout sets duration to transmit time plus four seconds. Furthermore, the CPU363 allows switching between protocols on a given port. This flexibility supports multi-vendor device integration. Engineers can change from SNP to Serial I/O through COMMREQ commands.
Key Technical Specifications for Integration
The CPU363 requires 890 milliamps from the 5 VDC power supply. It operates within a 0°C to 60°C ambient temperature range. The module weighs approximately 0.4 kilograms. Register memory configures in 128-word increments. Maximum %R capacity reaches 32,640 words with Control version 2.2. This capacity provides ample space for ASCII string storage. Firmware Release 9.0 or later supports floating-point math operations. The CPU includes a battery-backed clock for timestamp functions. These features enhance data logging capabilities for label applications.
Author Insight: Why Raw ASCII Still Matters in Industrial Automation
Many engineers assume that modern PLCs and DCS platforms have replaced legacy serial devices. However, raw ASCII communication remains vital in factory automation. Label printers, barcode scanners, and weigh scales often rely on proprietary command sets. Therefore, the IC693CPU363 with Serial I/O protocol offers a practical bridge. In my experience, this approach reduces hardware costs and simplifies wiring. Moreover, it avoids the need for external protocol converters. As a result, maintenance teams can deploy and troubleshoot systems faster.
Application Case: Label Printing on a Packaging Line
Consider a packaging line that applies date codes to cartons. The control system uses a Series 90-30 PLC with an IC693CPU363. Port 3 connects to a serial label printer. The ladder program uses COMMREQ Write Bytes to send ASCII strings. Each string contains the date, batch number, and operator ID. The printer receives the data and prints a label. This setup eliminates a separate print controller. Furthermore, it synchronizes printing with conveyor speed. Engineers can adjust the timeout value to match line throughput.
Solution Scenario: Integrating Multiple Serial Peripherals
A single IC693CPU363 can manage several serial devices over time. You can switch Port 3 between SNP and Serial I/O modes. However, only one protocol runs at a time. Therefore, plan your communication schedule carefully. For example, use SNP for programming and diagnostics. Then switch to Serial I/O for production printing. This flexibility supports multi-vendor environments. It also extends the life of existing GE Fanuc hardware. As a result, plant managers gain more value from their installed base.
Frequently Asked Questions
Q1: Can I use Port 3 for both SNP and Serial I/O simultaneously?
No. The IC693CPU363 allows only one protocol per port at a time. You must switch modes through COMMREQ instructions. Therefore, plan your communication tasks sequentially.
Q2: What is the maximum number of characters per Write Bytes call?
A single Write Bytes call transmits up to 250 characters. For longer messages, break the data into multiple calls. Moreover, ensure the %R registers remain unchanged during transmission.
Q3: Which baud rates work best for serial label printers?
Most industrial label printers operate at 9600 or 19200 bps. However, always check the printer manual. Some models support higher speeds, but reliability may vary with cable length.
Q4: How do I set a timeout for Serial I/O communication?
A 30-second timeout is a reasonable default. A zero timeout sets duration to transmit time plus four seconds. Choose a value that matches your production cycle.
Q5: Does the IC693CPU363 require special firmware for raw ASCII?
Firmware Release 9.0 or later supports floating-point math and Serial I/O. However, raw ASCII mode itself depends on COMMREQ configuration. Always verify your CPU firmware version before deployment.
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