Omega CN1166 Video Game Controller User Manual


 
Number. The contents of the remainder of the message depends upon the
function number.
In most cases the instrument is required to reply by echoing the address and
function number, together with an echo of all or part of the message received (in
the case of a request to write a value or carry out a command) or the information
requested (in the case of a read parameter operation). Broadcast Messages (to
which the controller responds by taking some action without sending back a reply)
are supported at instrument address zero. Commands which can be broadcast
are marked with the symbol
B.
Data is transmitted as eight-bit binary bytes with 1 start bit, 1 stop bit and
optional parity checking (None, Even or Odd).
A message is terminated solely by a delay of more than three character lengths at
the given Baud Rate, and any character received after such a delay is treated as a
potential address at the start of a new message.
The following individual message formats apply. Since only the RTU form of the
protocol is being supported, each message is followed by a two-byte CRC16.
Details of how the checksum must be calculated are given at the end of this
section.
A. Read Coil Status (Read n Bits) 01/02
The message sent to the controller will consist of 8 bytes, as follows:
The normal reply will echo the first two characters of the message received, and
will then contain a single-byte data byte count, which will not include itself or the
CRC. For this message, there will be one byte of data per eight bits-worth of
information requested, with the LSbit of the first data byte transmitted depicting
the state of the lowest-numbered bit required.
4-2 Volume II O077-4
Addr. Func.
Addr. of
1st Bit
No. of bits
CRC16
1/2
HI HI HILO LO LO
Addr. Func.
Count 1 - 8
9 - 16 17 - 24
Last
CRC16
1/2
HI LO