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 acknowledgment (see example).
• Bit 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 the register mode

MSB

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

Examples for the register communication

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).

Sample 1

Reading register 8 in the BK2000 with a KL5121 and the end terminal:

If the following bytes are transferred from the controller to the terminal,

The terminal returns the following type identifier (0x1401 corresponds to unsigned integer 5121).

Sample 2

Writing of register 31 in the BK2000 with an intelligent terminal and the end terminal:

If the following bytes (user code word) are transferred from the controller to the terminal,

the user code word is set and the terminal returns the register address with the bit 7 for register access as acknowledgement.