Register communication

Register access via process data exchange

  • Bit 7=1: Register mode
    If bit 7 of the control byte is set, the first two bytes of the user data are not used for process data exchange but written into the register set of the terminal or read from it.
  • Bit 6=0: read, bit 6=1: write
    Bit 6 of the control bytes is used to specify whether a register should be read or written.
    • Bit 6=0: A register is read without changing it. The value can be found in the input process image.
    • Bit 6=1: The user data are written into a register. The process is complete once the status byte in the input process image has returned an acknowledgement (see example).
  • Bits 0 to 5: Address
    The address of the register to be addressed is entered in bits 0 to 5 of the control byte.

Control byte in register mode (REG=1)











REG = 0: Process data exchange
REG = 1: Access to register structure

W/R = 0: Read register
W/R = 1: Write register

A5..A0 = register address
Addresses A5...A0 can be used to address a total of 64 registers.

Register communication 1:
Register mode control byte

The control or status byte occupies the lowest address of a logical channel. The corresponding register values are located in the following 2 data bytes. (The BK2000 is an exception: here, an unused data byte is inserted after the control or status byte, and the register value is therefore placed on a word boundary).