KROHNE VFM 5090 EN User Manual
Page 23
5.7.2 OUTPUT TYPE
1. RS-232
OUTPUT
The RS-232 output option provides a means for communication of measured values to remote system. At present,
this communication is in one direction only [from VFM 5090(I) to remote system]. Measured values as well as
Error Messages which appear on the instrument display in the normal measurement mode are output on RS-232
line. When the RS-232 output option is present, the usual frequency output function cannot be used.
1.1 RS-232
OUTPUT
The RS-232 output is galvanically isolated from all inputs and output circuits but not from current output.
Therefore, only one grounded receiver may be connected to either RS-232 output or current output. Note that
connecting RS-232 to IBM PC/compatibles will ground the RS-232 output.
·
·
·
Operating data for RS-232 output is not programmable as in case of current or frequency output. VFM
5090(I) always uses the following operating data : 1 Start bit, 8 Data bits, No Parity, 1 Stop bit at a baud rate of
1200 bits/sec.
Connection diagram for RS-232 output is given below. Please note that the RS-232 output uses the same
terminals as used by the Frequency output. Consequently, when the RS-232 option is present, frequency output
function can not be used.
5
+
6
-
4
RXD
4.1
TXD
4.2
GND
1.2 CHARACTER
FORMAT
Measured values or Error messages which appear on instrument display in normal measuring mode are coded as
series of 8-bit characters or “bytes”. These are transmitted serially, using a conventional UART (Universal
Asynchronous Receiver/Transmitter) function to serialize each byte. As in RS-232 or other asynchronous
communication, a start bit and stop bit are added to each byte. This allow the receiving UART to identify the start
of each character.
A single 8-bit byte is sent as the following sequence of 1’s and 0’s.
0 DO D1 D2 D3 D4 D5 D6 D7 1
Start bit <---------------------8 Data Bits -----------------------> Stop bit
Baud Rate is 1200 bits/sec. All characters are encoded in ASCII character format.
1.3 DATA
FORMAT
Format for transmitting Measured values or Error messages is as follows :
Measured
Value
<SP>
<SP>
unit
<CR> <LF>
#nn Err#
<SP>
<SP>
error
mesg.
<CR> <LF>
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