Category Archives: Communication Protocols

Behind every Forward_Open is one object. Behind every Forward_Close, every Unconnected_Send, every “connection timeout,” every “out of connections” error — one object. The Connection Manager Object (Class 0x06) is the CIP object that allocates and manages all the connection resources in a device. If Forward_Open is the service, the Connection Manager Object is what answers the door. This… Read More: CIP Connection Manager Object Explained (Class 0x06) »

When your I/O block reports “Link Down,” when error counters spike in Studio 5000, when a DLR ring takes longer than expected to converge — the data you need lives in the Ethernet Link Object, Class 0xF6. It’s the CIP object that holds every Ethernet-layer diagnostic on every EtherNet/IP device: link status, link speed, duplex mode, MAC address,… Read More: CIP Ethernet Link Object Explained (Class 0xF6) »

Every EtherNet/IP device has an IP address. Every device has a subnet mask and a gateway. Every device decides whether to get its address from DHCP, BOOTP, or static configuration. Every device that participates in multicast I/O has a multicast address range. All of this lives in one CIP object — the TCP/IP Interface Object, Class 0xF5. When… Read More: CIP TCP/IP Interface Object Explained (Class 0xF5) »

Every CIP I/O connection has a transport class — a single nibble in the Forward_Open Transport Class Trigger byte that decides how the connection behaves. Class 0, Class 1, Class 2, Class 3 — engineers see these terms in Studio 5000, in Wireshark captures, in product documentation — but rarely with a clear explanation of what each one… Read More: CIP Connection Types Explained: Transport Class 0, 1, 2, and… »

Every CIP device has one. Every browse of an EtherNet/IP network reads from it. Every Forward_Open validates against it. Every “what is this device” query touches it. The Identity Object (Class 0x01) is the most-accessed object on every CIP device — yet most articles barely cover it. This article fixes that. If you have ever wondered where Studio… Read More: CIP Identity Object Explained: How Every EtherNet/IP Device Identifies Itself »

An EDS file is a device’s résumé. It is plain text, it ships with the hardware, and your configuration software reads it so it does not have to know anything about your device in advance. Two industrial worlds use the same three letters for completely different files. CANopen has one EDS format. EtherNet/IP has another. They share an… Read More: EDS File Explained: CANopen and EtherNet/IP Device Files »

When a ControlLogix PLC reads inputs from a 1734-AENT Point I/O block, it does not read each input one by one. It reads one big block of bytes that contains every input in a defined order. That block is an Assembly Object instance. The Assembly Object is the mechanism CIP uses to bundle scattered data — input bits,… Read More: CIP Assembly Object Explained: How EtherNet/IP Devices Bundle I/O Data »

Every CIP I/O connection in the world starts with one service: Forward_Open. The PLC sends it to a remote drop, the drop validates it, and if everything checks out, the cyclic exchange begins. If something does not check out, the Forward_Open returns an error and the connection never opens — the device is invisible to the PLC until… Read More: CIP Forward_Open Service Explained: How Every EtherNet/IP Connection Starts »

When you read an attribute from a CIP device, the bytes you get back have a type. When you write a value, you must encode it in the right type or the device returns an error. This page is the complete reference for every CIP data type defined by ODVA’s CIP Networks Library Volume 1, Appendix C. CIP’s… Read More: CIP Data Types Complete Reference: Elementary, String, Time, and Structured… »

Every CIP message starts with a one-byte service code. That byte tells the target device what to do — read an attribute, write an attribute, open a connection, reset, save configuration. This page is the authoritative reference for every CIP service code defined by ODVA’s CIP Networks Library Volume 1, Appendix A. If services are the verbs of… Read More: CIP Service Codes Complete Reference: Common Services and Object-Specific Codes »