The interface with the designation “RS-485” is intended for the connection of a Pfeiffer Vacuum display
and control unit (DCU or HPU) or an external computer. The connections are galvanically safe and are
isolated from the maximum supply voltage for the electronic drive unit.
Designation
Value
Serial interface
RS-485
Baudrate
9600 Baud
Data word length
8 bit
Parity
none (no parity)
Start bits
1
Stop bits
1
Tbl. 7:
Features of the RS-485 interface
Connecting a Pfeiffer Vacuum display and control units or PC
► Use the connection cable from the control unit scope of delivery or from the accessories program.
► You can connect one external control unit to the RS-485 interface.
► You can connect a USB interface (PC) via the USB/RS-485 converter.
PC
D-Sub
1
2
3
4
Fig. 16:
Cross-link via connection RS-485 using connection cables and accessories
1 Connection cable with RS-485
3
M12 to M12 extension cable
2 Y-connector for RS-485
4
USB RS-485 converter
Networking as RS-485 bus
The group address of the electronic drive unit is 902.
1. Install the devices according to the specification for RS-485 interfaces.
2. Make sure that all devices connected to the bus have different RS-485 device addresses
[P:797]
.
3. Connect all devices to the bus with RS-485 D+ and RS-485 D-.
6.3 Pfeiffer Vacuum protocol for RS-485 interface
6.3.1 Telegram frame
The telegram frame of the Pfeiffer Vacuum protocol contains only ASCII code characters [32; 127], the
exception being the end character of the telegram C
R
. Basically, a master
(e.g. a PC) sends a tele-
gram, which a slave
(e.g. electronic drive unit or gauge) responds to.
a2
a1
a0
*
0
n2
n1
n0
l1
l0
dn
...
d0
c2
c1
c0
C
R
Interfaces
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