Product manual
100-M0131X1A 02/10/10 25 of 31
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4. Control Protocols
The following section describes the control protocol employed on the RS232 link for controlling
the VETA transmitters and Receivers.
Refer to corresponding manuals for low level commands list.
4.1 RS232 Control
The physical interface is RS232. Normal operation involves sending a packet from the control
device (normally a PC) to the device being controlled. If the packet satisfies an address integrity
check, then the controlled device will action the command and send a reply. For compatibility with
modems an ASCII style protocol is used. Ports are set for 8 bits, No parity, 1 stop bit.
4.2 Packet Structure
The following Table 11 and Table 12 show the packet structure send and receive.
The Sum check byte is the summation of all bytes in the packet, not including the start and end
bytes. Higher order bytes are ignored and the final byte result is modified to prevent ASCII control
characters being sent. Bit 7 (highest) is forced high. Status byte will indicate command performed
OK, or indicate an error.
ASCII Meaning
1 All OK
E General error, Command could not be actioned.
Typically E will be returned if the message is formatted incorrectly (separators in wrong place) or if
commands are in upper case, or if commands do not match against the allowed list of commands,
or if the checksum is wrong.
Addresses in the range 0001 to 9998 are for general use. Address 0000 is reserved and 9999 is a
broadcast address. I.e. any device will reply to this address. Its reply will contain its own specific
address.
All data in the transmitter and receiver is stored as one of 5 data types: Double, String, List, Integer
or Hex Integer. The data type dictates the contents of the data section of the reply.
List – 1 byte for sending. Value is hexadecimal coded as ASCII. 2 byte reply. Reply
represents index into original choice list. E.g. Reply 02 indicates entry 2 in original list.
Double - variable length. Reply always contains decimal point and 4 decimal places, can
have 1 to 3 digits before decimal.
Integer - 6byte reply. Integer value with stuffed with preceding zeros. e.g. GOP reply
000012 = GOP length 12
String - Variable length. Reply is string excluding null terminator
Hex Integer – 8byte Hex reply