BECKHOFF BK2000 - Manual (Page 27)

Annex
BK2000 27
Representation of the analog signals in the
process image
Three input bytes and three output bytes of the process image are needed
for each analog channel. Two bytes represent the value as signed integer
(two's complement), i.e. 15 bits with sign. The data format is used
regardless of the actual resolution. As an example: with a resolution of 12
bits, the four least significant bits are irrelevant. The least significant byte
has control and status functions. Various operating modes can be set with
the control byte. The six least significant bits can be used as addressing
bits. Addressing serves to read and write a register set with string
communication. The register set has 64 registers.
I/O bytes of an analog
Output byte 1 Output byte 0 Control byte not used
channel in the
process image Input byte 1 Input byte 0 Status byte not used
Bit
Meaning of the BIT 7 0 = NORMAL MODE, 1 = CONTROL MODE
control/status byte for BIT 6 0 = READ, 1 = WRITE
access to the BIT 5 Register address, MSB
register model BIT 4 Register address
BIT 3 Register address
BIT 2 Register address
BIT 1 Register address
BIT 0 Register address, LSB