Frame Types - Hydronix Hydro-View HV02 User Manual

ASCII HEX MODE
Field
REQUEST
DATA
CHECKSUM
ETX

Frame types

The master device issues request frames. These frames either solicit data from the slave
or send information to the slave for it to process, or a combination of both. The slave can
respond to a request in one of four ways...
It processes the request and issues an acknowledge frame back to the master.
It processes the request and issues a reply frame back to the master containing some
data.
It does not process the request because the request was invalid although not
corrupted. An acknowledge frame is then sent containing an error code.
It does nothing. In this case, the slave may have detected an error (usually corruption)
but cannot reply because to do so may result in further errors. An example of this may
be a faulty checksum in the request - the slave cannot reply here since it would not be
certain that the station number itself had not been corrupted. In this case the slave will
ignore the faulty frame and attempt to synchronise to the next STX character.
Request frame format
Issued by the master station. Format as per table in Basic Frame Format above.
Acknowledge frame format
Issued by slave stations.
The station number has the top bit set as described in Basic Frame Format above.
The request field is returned unaltered.
The data field is a single byte (two hex digits) code from the following table...
Code
00
01
76
HYDRO-VIEW USER GUIDE D0022 REV 1.06
Format
Two
ASCII-Hex
characters
Two
ASCII-Hex
characters per
byte of data
Two
ASCII-Hex
characters
03
Mnemonic Description
OK The request frame was received and processed without
error.
BAD_REQUEST The request field of the request frame was not
understood by the slave. This may mean that the
version number of the firmware running in the slave is
out of date.
Description
Two ASCII Hex characters representing a request to
be processed. Valid request codes are in the range
01-FF, but only certain commands will be recognised
by the Hydro-View - see below.
As required by the COMMAND field.
Data entities larger than one byte are transmitted
low-byte first in keeping with the order used by Intel
family processors (such as those in the IBM-PC)
which allows data to be streamed directly into a 'C'
data structure (for example) without re-ordering of
data. Motorola family processors will need to
assemble the data bytes accordingly for both
transmission and reception.
Byte-wise exclusive-OR (XOR) of all characters from
the station number to the end of data inclusive.
End of frame.