STATUS SCIENTIFIC CONTROLS
Installation, Commissioning & Routine Gas Testing
FGD10A Oxygen / Toxic Gas Detector
TD18/002
Issue:
16
Change Note:
1904
Page 39
7.3. Frame Structure
The start of a frame is indicated by a DLE byte followed by the type
of frame to follow (RD, WR, ACK, NAK, DAT). The end of frame is
indicated by a DLE byte followed by an EOF byte.
Note:
Each of the constants has bit 4 set and so is slip-resistant
(i.e. if shifted this bit will be out of position). The values have a
Hamming Distance of 2 (each code is at least 2 bits different from
every other code).
Any DLE bytes that occur
between a frame’s start and end are
prefixed with another DLE (
byte-stuffing
).
Following the EOF is a 16-bit checksum of the entire frame, each
byte is added to produce the checksum.
7.4. Variables
Each piece of accessible data on a device is referred to as a
Variable
. Each
variable is referenced by a
Variable ID
. A variable ID may be any number of
bytes long.
The available Variables and their corresponding Variable IDs depend on the
type of device, but here are a few examples for the FGD10A:-
General Configuration
0x00
Live Data
0x01
Zero Sensor
0x02
Span Sensor
0x03
Version Information
0x04
Firmware Update
0x05
The structure of the data returned in each variable usually depends both on
the type of device and the version of firmware running on the device.
Refer to device documentation for more information.
