LEYBOLD 157 89, Manual

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- Transmission data TxD Pin 2 Opposite side:
Receive data
- Receive data RxD Pin 3 Opposite side:
Transmission data
- Signal ground GND Pin 5 Opposite side:
Signal ground
The signals DTR and RTS are generated by the A-series
instrument in order to offer correct status conditions for
the opposite side; the A-series instrument itself does not
requires these signals.
It is strongly recommended to use a screened interface
cable, especially if there is the likelihood of electroma-
gnetic interference. In this case the shield of the scree-
ned cable should only be connected on the side of the A-
series instrument (Pin 9).
In the event of very high levels of electromagnetic inter-
ference and potential differences between the A-se-ries
instrument and the opposite side (also the sensor side)
a potential equalization line of sufficient cross section
should be connected between the various frame grounds
(a 4 mm screw terminal is provided on the rear of each
A-series instrument for this purpose).
Alternatively also RS 232 isolation amplifiers or fibre
optical links may be used to prevent large equalization
currents from flowing. Such equipment is commercially
available.
3.3.1.2 Baud rate and data format
When starting up the instrument in connection with a
computer or terminal the correct baud rate and data for-
mat must be set up on the connected equipment.
3.3.1.3 End character
In the remote control mode the characters <CR> (carria-
ge return; ASCII code: 13d and line feed; ASCII code:
10
d
) are used. The character <LF> (line feed; ASCII
code: 10
d
) is always ignored by the A-series instrument.
With one exception each character string sent to the A-
series instrument must be terminated with <CR>. The
only exception is the reset command which consists only
of one character <ESC> (see also Section 2.3.1.5).
In the other direction there is no exception; all characters
transmitted by the A-series instrument in the remote con-
trol mode are terminated by <CR>.
In the case of a missing or incorrect end character <CR>
the interface will usually not operate properly.
3.3.1.4 Acknowledgement character
In the remote control mode, the A-Series instrument will
respond to each string it receives and which has been
terminated by the end sign <CR>, with one of the ack-
nowledgement characters <ACK> or <NAK>.
<ACK> (ASCII code: 6
d
) means that the received com-
mand has been detected, the parameters are acceptable
and that the command which has been received can be
run in the current operating mode.
<NAK> (ASCII code: 21
d
) means that a variety of errors
may have occurred during the transmission.
- General transmission fault, interference, wrong baud
rate, wrong number of start, stop or data bits
- Wrong command or command can not be run at the
moment (for example MIS instead of MES for request to
send measurement data)
- Wrong direction command (R/W)
- Parameter not within the correct range, not permissible,
incomplete, wrong number, not or incorrectly separated
(: instead of ;)
It must always be taken in to account that the instrument
will only be ready to receive and process the next com-
mand after receiving the <ACK> or <NAK> character
and a possibly demanded reply character string.
Any characters which are sent to the instrument after the
end sign and before the acknowledgement character is
sent will be ignored.
Example for a CM 31
Communication where, for example, the measurement
value is read from DM channel 1 followed by setting the
PM channel to argon whereby one character is not trans-
mitted correctly with subsequent correction by the con-
trol computer:
The control computer transmits „MES R TM 1 <CR>“
Time required for processing by the
A-series instrument
A-series instrument transmits „<ACK><CR>“
Time required for processing by the
A-series instrument
A-series instrument transmits
„TM1:MBAR :3.72E+01<CR>“
Control computer transmits
„GBS W PM1 ARGON<CR>“
Time required for processing by the
A-series instrument
A-series instrument transmits „<NAK><CR>“
Control computer transmits
„GBS W PM1 ARGON<CR>“
Time required for processing by the
A-series instrument
A-series instrument transmits „<ACK><CR>“
Note
The time required by the A-series instrument to process
the interface commands may be as long as 500 ms,
however, normally this time will be much shorter.
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