BECKHOFF BC8000 - Manual (Page 27)

Appendix
BC8000 27
Representation of analog signals in the process image
Every analog channel consists of three input bytes and three output bytes
but, in the standard case, one analog channel only occupies one data word
in the process image. These two bytes represent the value as an unsigned
integer, i.e. 15 bits with a sign. The data format is used independently of
the actual resolution. For example: in the case of the resolution of 12 bits,
the four least significant bits are irrelevant. Using the KS2000 configuration
software, it is possible to insert the third byte into the process image for
any chosen channels. The least significant byte has control and status
functions. Various operating modes can be set with the control byte. The 6
least significant bytes can by used as addressing bits. Addressing serves
to write and read the register set. The register set has 64 registers and
permits setting of various operating parameters, for example selection of a
thermocouple type or representation of the value in a different number
format. For further information, refer to the corresponding documentation of
the terminals.
Output byte 1 Output byte 0 empty Control byte I/O bytes of an analog
channel in the process
image
Input byte 1 Input byte 0 empty Status byte
BIT 7 0 = NORMAL MODE, 1 = CONTROL MODE
BIT 6 0 = READ, 1 = WRITE
BIT 5 Register address, MSB
BIT 4 Register address
Significance of the
control/status bytes
for accessing
the register model
BIT 3 Register address
BIT 2 Register address
BIT 1 Register address
BIT 0 Register address, LSB
63 Register set of an
analog channel
47
31
15
User area
16 0
OFF SET
GA IN
Factory settings
SoftwareVers
Type
0 Length Type
Secondary process image
The meanings of the registers and of the status bytes are explained in the
bus terminals' corresponding data sheets. The structure of the module is
identical for all bus terminals featuring more extensive signal processing.