
10.2 POII - Host Controlled Transmit Mode
This mode requires a host computer or PLC to poll the instrument to obtain display or other
information or reset various setpoint parameters. Terminal communications software is required
when using POLL mode with a PC. Data is in ASCII format with 8 data bits + 1 stop bit.
Addresses are offset by 32 Dec. i.e. address 1 is 33 Dec. When polling the instrument it is essential
that the command characters are sent with less than a 10mS delay between them. This normally
means that each command line must be sent as a whole string e.g. <STX>PA<CR>is sent as
one string rather than <STX>on one line followed by P etc. If testing using at terminal program
this is normally achieved by allocating a command string to a function key. Whenever the function
key is operated the whole string is sent. The format used is ASCII (8 data bits + 1 stop bit) so,
for instance, if address 1 is used then the string <STX>PA<CR>must be put into the terminal
program as:
∧BP!∧M
where: ∧B is the ASCII character for STX
P is the command line to transmit the primary display value
! is the ASCII character for address 1 (33 Dec of 21 Hex)
∧M is the ASCII character for CR
A typical format for the host command is as follows:-
<STX>CA<CR>(Standard read etc.)
<STX>CA<CR>N<CR>XYYYY (Set Value Command)
Where: <STX>is Start of Text Character (2 Dec, 02 Hex, ∧B ASCII)
C is the command character (see following commands)
A is the unit address (Range: 32 to 63 Dec,
20 to 3F Hex, “SPACE” to ? ASCII
the address is offset by 32 Dec, 20 Hex)
<CR>is Carriage Return (13 Dec, 0D Hex, ∧M ASCII)
N is the setpoint number in ASCII
e.g.: 1 for alarm 1 etc.
X SPACE for positive and “-” for negative
YYYY is the setpoint value in ASCII
The POLL commands available and instrument responses are as follows:
1. Transmit Primary Display Value: <STX>PA<CR>
e.g. ∧BP!∧M using a terminal program (address 1). Instructs unit to return the primary display
value. The primary value is the main reading.
Format of returned data is:
<ACK>PAXYYYY<CR>
Where: <ACK>is Acknowledge (6 Dec, 06 Hex)
P echo command received “P” (80 Dec, 50 Hex)
A is the responding units address
X SPACE for positive and “-” for negative
YYYY is the display value in ASCII
<CR>is a Carriage Return (13 Dec, 0D Hex)
The number of display characters returned depends on the number of display digits present. If the
decimal point is non zero then it will be sent in the appropriate place as “.” (46 Dec, 2E Hex). The
primary display for most instruments is the main reading, in some instruments the main reading
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