Pressure Systems, Inc. Model 9116 User’s Manual
Page 21
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3.1.2.4
Datum Fields
Any
datum
fields in a command generally contain data to be sent to the module, usually
specified by a
position
field bit map. In some commands (when data are received from a module
instead) no datum fields are required in the command itself but the
position
field bit map is still
used to specify the order that data are returned in the command’s response. In either case, the
order bits are set (to 1) in the
position
field bit map (highest channel # to lowest channel#, left to
right) is the order these datum fields are received or sent.
Each
datum
field may be variable in length, whether part of the command itself or the
command’s response. In its most common format, a
datum
begins with a
space
character (‘ ’),
and is followed by an optional sign, decimal digits, and a decimal point, as needed (e.g., ‘
-
vv.vvvvvv
’). For other formats it may be a hex digit string or pure binary number.
3.1.2.5 Format
Field
Some commands, that either send data to a module (as command parameters), or cause the
host to receive data (via command’s response), have an extra
format
parameter
(f
digit)
appended to (or specified in) the
position
field. This parameter, when specified (or implied by
default), governs how internal data are converted to/from external (user-visible) form.
•
The most common format (
f=0)
causes each datum (in command or response) to be
represented as printable ASCII numbers externally (with optional
sign
and
decimal point
as needed). Internally, the module sets/obtains each converted datum to/from a single
precision binary (32-bit) IEEE float
•
Some formats (
f
=1, 2, 5) encode/decode the internal binary format to/from ASCII
hexadecimal external form. Some of these “hex dump” formats provide an external hex
bit map of the internal binary value (float or integer as appropriate). Format 5 may
encode/decode the internal float value to/from an
intermediate
scaled binary integer
(e.g., float value * 1000 into integer, then to/from a hex bit map).
•
Two special “binary dump” formats (
f
=7 and
f
=8) may be used by some commands to
accept/return binary data directly from/to the user’s command/response. Such values
are not user-readable in their external form, but are directly machine readable and
provide highly compact storage without any accuracy loss due to formatting. Use of
these formats allows both the module and host program to operate in their most efficient,
low overhead mode. Format 7 returns the most significant byte first (i.e.,
big endian
).
Format 8 returns the least significant byte first (i.e.,
little endian
).
See the individual command descriptions for the formats a particular command recognizes.
