The AD-AAB 20 GX provides 2-channel output of analog signals. The device communication is realized using the MODBUS RTU protocol. The analog setpoints can be set via implemented MODBUS commands.
The power supply and the RS485 bus connection are possible via the rear DIN rail connector. The device is equipped with two rotary coding switches with which the bus address can be set on the device.
The operating voltage is indicated by a green LED. The data communication is signaled with a yellow LED. An optical search function allows the localization of a single device in a network. For this purpose, the green LED is set in a time-limited flashing mode, between 1 and 255 seconds.
As well as interface settings as well as the device address can be modified during operation by means of Modbus commands. All Modbus register addresses and associated commands are listed in the document attachment.



Specification of analog process signals for control purposes.

Specific characteristics

  • Two analogue outputs can be used as voltage or current input
  • Galvanically isolated RS485 bus interface
  • Parameterizable interface settings
  • Hardware switch for device address
  • Galvanically isolated switching power supply
  • Can be parameterized with PC via AD Studio configuration software
  • Status LED for operating voltage and data communication
  • Optical search function
  • Modbus master mode

Business data

Order number
Rail connector
Artnr: AD-GX-Connector
Zur Durchschleifung von Versorgungsspannung und RS485-Bus
Aufrastbar auf Tragschiene
(DIN EN 50022).
Customs tariff number / country of origin 8543 70 90 / Deutschland


Data sheet pdf en-aab20gx.pdf (216 kB)
Tender text zip (10 kB)
Safety instructions pdf ad-safety-instructions.pdf (43 kB)

Technical specifications

Current outputs
Range 0 ... 20 mA
Output load Max. 450 Ohm
Voltage outputs
Range 0 ... 10 V
Output load Min. 10 kOhm
Signal output
Channel counts (U/I) 2
Basic accuracy < +/- 0,3 %
Temperature influence 100 ppm/K
Resolution 12 bit
Transmission behaviour
Response time Max. 15 ms
Software protocol Modbus-RTU
Data format 19200, e, 8, 1
Max. bus users 99
Bus termination 120 ohms both sides at the end
Max. length of bus 500 m (no spur lines)
Cable Twisted and shielded
Supply voltage 18 ... 30 V DC
Max. power consumption 1400 mW (24V DC)
Dimensions (WxHxD) 6,2 x 92 x 101 mm³
Manner of fastening DIN rail mounting 35mm, EN 50022
Type of protection IP 20
Connection method Screw clamp
Bolting torque terminals 0,5 Nm
Wire cross section Max. 2,5 mm2
Weight ~ 70 g
Environmental conditions
Permissible ambient temperature -10 ... +50 °C
Storage and transport -10 ... +70 °C (no condensation)
Product family standard 1) EN 61326-1
Emission 2) EN 55011, CISPR11 Cl. A, Gr. 1
1) During checking, slight signal deviations are possible.
2) Warning:
This device is not intended to be used in residential areas and can not ensure adequate protection of radio reception in such environments.
Electrical safety requirements
Product family standard EN 61010-1
Galvanic isolation, test voltages
RS485 bus / power supply 1,5 kV, 50 Hz (1 min)
Analog output / power supply 1.5 kV, 50 Hz (1 min)
Analog output / RS485 bus 1,5 kV, 50 Hz (1 min)
Analog outputs between themselves 0,5 kV, 50 Hz (1 min)
Protection circuits
Power supply Electrical surge and reverse current protection

Block and wiring diagram




CAD / CAE Daten

CAD model is not yet available for this product.

The CAD product overview can be found at:

Display and operating elements

Designation LED Meaning
On green Power supply
D yellow RS485 Communication
RS485 Address switch(01...99)

Modbus Communication

The AD-AAB 20 GX contains a RS485 bus interface on which the Modbus RTU protocol is used. All control functions of the device can be executed via this bus interface. The preset standard data format is 19200,e,8,1. Adaptation to a different data format is possible at any time. The bus address (1...99) is set to the side-mounted rotary switches. The address 0 is not permitted for the bus operation. However, on this zero position the device is accessible only via the standard data format (19200, e, 8.1). The position 0 thus represents a service position, the example can be used during parameterization error.

The AD-AAB 20 GX supports two Modbus functions. These are the functions "Read Holding Registers" (0x03) and "Write Holding Registers" (0x10). With the "Read Holding Registers" function data can be read from the device and written with "Write Holding Registers" data. The individual register width is 16 bits. Please see the Modbus specification for detailed explanations of the Modbus communication. This is online available for free and can be downloaded from the Adamczewski homepage.

The following Modbus data are accessible via the RS485 bus:

Start address Reg. number Name Datatype [Code] = Value read write
40501 1 Address switch U16 1...99...247 yes yes
40502 1 Flashing function U16 0/1...255 yes yes
40901 2 Analog output U1 FLOAT 0...10V no yes
40903 2 Analog output I1 FLOAT 0...20mA no yes
40905 2 Analog output U2 FLOAT 0...10V no yes
40907 2 Analog output I2 FLOAT 0...20mA no yes
40909 2 Scale out U1 FLOAT +/- Scale value no yes
40911 2 Scale out I1 FLOAT +/- Scale value no yes
40913 2 Scale out U2 FLOAT +/- Scale value no yes
40915 2 Scale out I2 FLOAT +/- Scale value no yes
44201 2 Scale begin Channel 1 FLOAT +/- Scale range yes yes
44203 2 Scale begin Channel 2 FLOAT +/- Scale range yes yes
44205 2 Analog begin Channel 1 FLOAT 0...100 % yes yes
44207 2 Analog begin Channel 2 FLOAT 0...100 % yes yes
44211 2 Scale end Channel 1 FLOAT +/- Scale range yes yes
44213 2 Scale end Channel 2 FLOAT +/- Scale range yes yes
44215 2 Analog end Channel 1 FLOAT 0...100 % yes yes
44217 2 Analog end Channel 2 FLOAT 0...100 % yes yes
42901 1 Baud rate U16 Index, see list below yes yes
42902 1 Parity U16 [0]=even; [1]=odd; [2]=no yes yes
42903 1 Modbus Master U16 0/1 yes yes
49102 1 Device reset U16 0 no yes
49105 6 Device type String AAB20GX yes no
49119 1 Firmware version U16 MSB/LSB yes no

Coding baudrate list
index 0 1 2 3 4 5 6 7 8 9
baud 2400 4800 9600 14400 19200 28800 38400 57600 76800 115200

After changing the interface parameters, a device reset is required.

Modbus master mode
The device can even work in Modbus master mode to transfer data between any devices within an RS485 line.
For Modbus master operation, starting with Modbus register 40611, there are 37 consecutive data transfer sets,
with 5 configuration registers each.

Start address Reg. number Name Datatype [Code] = Value read write
40611 1 Source address [1] U16 1...98 ja ja
40612 1 Source register [1] U16 nnnnn ja ja
40613 1 Target address [1] U16 1...99 ja ja
40614 1 Target register [1] U16 nnnnn ja ja
40615 1 Register count [1] U16 1/2 ja ja
40791 1 Source address [37] U16 1...98 ja ja
40792 1 Source register [37] U16 nnnnn ja ja
40793 1 Target address [37] U16 1...99 ja ja
40794 1 Target register [37] U16 nnnnn ja ja
40795 1 Register count [37] U16 1/2 ja ja

For the Modbus master mode, the parameter "Modbus master" must be activated and the address switch set to position 99.
Data transfer begins six seconds after activation or device restart.
A flashing green LED indicates a communication error.

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