5
5.1
COMMANDS
COMMAND FORMAT
Communication between the host or control processor and a PPT is accomplished by message trans-
fers, or commands and replies. Communications initiated by the host processor to one or more PPTs
are called
commands
and must begin with an ‘*’ or a ‘~’
header character
. All commands must be
terminated by a <cr> (carriage return or ENTER key). Communications initiated by a PPT to the
host are called responses or
replies,
and begin with one of ten unique header characters (2 for
ASCII, 8 for binary).
Commands may either
request information
from one or more PPTs such as read pressure, or
direct
action
to one or more PPTs such as change a configuration value or operating mode.
Typical PPT command format: *ddcc = nnn
<cr>
Where: *
is the command header character (a ‘~’ in one case)
dd
is the decimal address of the command message (00-99)
cc
is the command code. The command code characters can be one letter, two letters, or
a letter and a number. The letters are not case sensitive; i.e., either an upper case or
lower case may be used. The PPT will convert the character to upper case.
=
equal sign (required in some commands)
nnn
additional characters (required in some commands)
<cr>
carriage return (do not type, press the ENTER key)
Note:
For RS-485 mode, alternate headers are available. (see
MO
command)
For RS-232 mode, when manually applying commands to one or more PPTs which are in the continu-
ous send mode
(P2, P4, T2, T4),
the special header character ‘$’ should be used to suspend all PPT
transmissions while the command message is being typed. The ‘$’ is immediately followed by the
normal command format.
Also for RS-232 mode, if an erroneous command is sent to the PPT, it is echoed back to the host in
the same form it was sent. The only exception to this is when a group or global address command (ID
= 90 to 99) is sent such as *99S2=15<cr>. These addresses will always echo the command back to the
host processor after being read by all PPTs.
Commands are not executed until the carriage return is applied; therefore, any command message
may be re-entered at any time prior to the carriage return. To do this, type a ‘*’ followed by the
command, or press a carriage return and retype the command.
Only the minimum number of characters is required for command inputs to distinguish between
various command options. For example,
DU=MB
,
DU=MBAR
, or
DU=MBXYZ
will all set the
display units to millibar, since only the first two characters (MB) are needed. Also, when a parameter
value is entered that exceeds the stated range for that value, the parameter will be set to the maxi-
mum value for that range.
A special binary format command that controls the DAC analog output, uses a ‘~’ (tilde) header
character instead of an ‘*’ (asterisk). This command is sent in binary form, as opposed to ASCII, and
is a more efficient alternate to the standard command requiring less data to be transmitted (see
Section 5.4 for binary and ASCII descriptions). For this command, the ‘~’ has the same header
functional characteristics as the ‘*’ described above.
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