Dressler CESAR 1312, User Manual

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4-58 Communication Interfaces CESAR 1312 (E)
Dressler
®
HF-Technik GmbH
Data Encoding
The CESAR generator uses standard, little endian (least significant byte first)
architecture. However, Modbus/TCP registers use swapped words, or big
endian (most significant byte first) architecture.
For data contained in a single, 16-bit register, this difference simply means
that the byte order is reversed (byte 1, byte 0). For data that occupies multiple
registers, data must also be encoded least significant word first. For example,
a 32-bit value would be sent in the following order: byte 1, byte 0, byte 3, byte
2.
Note: In FC23, the portion of the packet containing AE Bus command bytes is
not reordered. These bytes are ordered exactly as they are for the
AE Bus command.
Data Monitoring and Configuration Changes With Multiple Clients
Multiple clients may send configuration information simultaneously. All
configuration commands in the CESAR generator are atomic, which prevents
erasing problems. However, one client may overwrite another's configuration
information. Using Modbus/TCP FC23
FC23 allows you to send any CESAR generator AE Bus command through the
Modbus/TCP interface, providing complete control of the system in a way that
directly corresponds to the AE Bus commands. (For a complete listing of the
AE Bus commands and their associated data, see
Table 4-16 on page 4-63 .
For AE Bus protocol information, see “AE Bus Protocol” on page 4-45 .)
To accommodate this use of AE Bus commands, the CESAR generator uses
some special values in the FC23 packet. The following sections describe the
packet format for FC23 send, receive, and exception error packets.
FC23 Send Packet Format
Table 4-12 describes the bytes contained in the FC23 send packet.
Note: If the CESAR generator rejects a command, it returns an exception 01
code.
Table 4-12. Packet format for FC23 send
Byte
Numbers
Purpose Value to Send
0 and 1 Transaction ID Not used (value is copied into reply)
2 and 3 Protocol ID 0
4 and 5 Number of
bytes following Count of bytes in packet, starting with
byte 6