GI74 is a proprietary communication protocol that was first produced in 1974; however it has been retained due to the fact that it has proven reliable in service and replacement part have been easy to obtain.


7 Application Layer GI74 Application Layer
6 Presentation Layer n/a
5 Session Layer n/a
4 Transport Layer n/a
3 Network Layer n/a
2 Link Layer n/a
1 Physical Layer RS232 / V.24 (PCM)

Supported Information Types

Control Direction
  • Single Command
Monitoring Direction
  • Single indication [1 Bit]
  • Double indication [2 bit]
  • Measured value [8 bit]
  • Measured value [11 bit]
  • Tap position [5 bit]

Protocol Features

  • Physical Layer

    PCM, half-duplex, 23 bit data words
    1 start bit, 16 data bits, 5 CRC bits, 1 stop bit

  • Application Layer

    Block or word interrogations of indications and measured values
    "Select before operate" transmission of commands

  • Address Space

    RTU address 1..255 depending on length (from 5 to 8 bits)
    Function address 0..15
    Block address 0..7
    Word address 0..7

Implemented Protocol Stacks

GI74, Slave

Applicable Products

  • ipConv

    Universal protocol converter for highest degree of flexibility