Dressler 13150 400 V, User Manual

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4-24 Communication Interfaces HPG 13150 400 V (A)
Dressler
®
HF-Technik GmbH
Prerelease version
Figure 4-17 shows the organization of these fields in the AE Bus message
packet. The subsequent paragraphs describe each field in detail.
Figure 4-17. Graphic representation of a message packet
AE Bus Header Byte
The first byte in each packet contains two pieces of information: five bits
contain the packet address, and three bits contain the data byte count. If the
message packet originates with the host computer (master), the address
specifies the packet destination (to a HPG generator, for example). If the
packet is going to the
Host , the address specifies the packet origin (from the
HPG generator). The address section of the Header field is five bits long (bits
3-7), which allows a total of 32 distinct addresses. Address 0 (zero) is
reserved for the network broadcast address; when this address is used in a
Host -originated packet, all units execute the packet (but do not respond to the
host).
The remaining three bits (bits 0, 1, and 2) are the length bits. These bits tell
the receiving unit how long the Data field is so that the unit can determine
when it has received the entire message. If the Data field contains more than
six bytes, the value of these three bits will be set to 7 (07h), and the Optional
length byte field will contain a value indicating the number of data bytes in the
Data field.
Note: The value of these bits refers only to the number of actual data bytes in
the Data field. Do not include the checksum byte when calculating the
value for these bits (see
“AE Bus Checksum Byte” on page 4-25 ).
AE Bus Command Number Byte
This one-byte field contains an 8-bit value from 0 to 255 (00h to ffh)
representing the command number. If the message packet originates with the
host computer, this value specifies the purpose of the message packet. If the