The KOYO R-21P-4129 is a CPU (Central Processing Unit) Module for the KOYO DirectLOGIC DL205 series of micro-modular programmable controllers. It is the brain of the PLC system, responsible for executing the user-written control program, managing I/O (Input/Output) modules, and handling communication.
Decoding the Part Number: R-21P-4129 J-03 #2
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R-21P: This is the core model identifier.
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R-21: Denotes the DL205 series rack/controller.
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P: Indicates this is the CPU module (as opposed to “C” for communication modules, etc.).
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4129: This is the specific variant code.
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4: Likely indicates the I/O capacity or memory size tier (this is a mid-range model).
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129: Specifies the features, including the type of processor, memory, and built-in ports.
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J-03: Typically a factory production code or hardware revision number.
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#2: Often indicates a packaging quantity or a specific kit version (e.g., includes manual or software).
Key Features and Specifications (Based on the DL205 Series R-21P CPU):
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Manufacturer: KOYO Electric / JTEKT (The automation division was formerly known as “KOYO Electronics” and is now under JTEKT Corporation’s “Controller Division”).
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PLC Series: DirectLOGIC DL205 (a very popular and long-standing series).
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CPU Type: Micro PLC, suitable for small to medium-scale automation tasks.
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Memory: Likely in the range of 6K to 14K words of user program memory (depending on the exact -4129 specification).
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Built-in Ports:
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Programming Port: A serial RS-232 port for connecting a programming device (PC) using software like DirectSOFT.
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Auxiliary Port: A second serial port (RS-232/RS-485 configurable) for connecting peripherals like HMIs (Human Machine Interfaces), bar code readers, or for peer-to-peer (DF1) communication with other PLCs.
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I/O Capacity: Can control a local base (rack) with multiple I/O modules (discrete and analog). The exact maximum depends on the CPU model.
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Programming Software: Programmed using DirectSOFT (now at version 6.x). Ladder Logic is the primary language.
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Communications: Can be expanded with various communication modules (Ethernet, DeviceNet, Profibus, etc.) for network connectivity.
This is a genuine KOYO (JTEKT) DirectLOGIC DL205 series CPU module, model R-21P-4129. This programmable logic controller (PLC) processor serves as the central brain for industrial automation systems.
Ideal for: Machine control, process automation, packaging lines, and material handling systems that utilize the legacy DL205 platform.
Key Attributes:
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Micro-Modular Design: Allows for flexible I/O configuration.
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Dual Serial Ports: For programming (RS-232) and peripheral/network communication (RS-232/485).
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Compatibile with DL205 I/O: Works with a wide range of discrete, analog, and special function modules.
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Programmed with DirectSOFT: Industry-standard ladder logic programming.



