Maxx GW4101

The device

The programmable maxx GW4101 mobile communication gateway for industrial applications collects and processes the information from your devices, machines and sensors, and transmits it via the expanded LTE network.

The basic unit (left part of the device) is described under maxx GW4100

The sensor interface expansion enhances the basic unit with interfaces for PT100/1000 temperature sensors and the widely used 4 – 20 mA current loop interface, as well as other digital inputs and outputs. The maxx GW4101 gateway is therefore ideal for transmitting measurements from the field to the head office or the cloud.

Interfaces

Pinout RS485 isolated

Description	Function	Label	Pin	Pin	Label	Function
#RS485	---	---	1	2	D+	IN D+
	ISO GND	IG	3	4	D-	IN D-

Pinout Digital IN/OUT

"Label" describes the labeling on the frontplate

"Signal" describes the reference to the Linux mapping

Description	Function	Label	Signal	Pin	Pin	Signal	Label	Function
#Isolated outputs	OUT 1	1A	ISO_OUT_A1	1	2	ISO_OUT_B1	1B	OUT 1
	OUT 2	2A	ISO_OUT_A2	3	4	ISO_OUT_B2	2B	OUT 2
#Isolated inputs	Iso Input 1-	1-	ISO_IN_N1	5	6	ISO_IN_P1	1+	iso Input 1+
	Iso Input 2-	2-	ISO_IN_N2	7	8	ISO_IN_P2	2+	iso Input 2+
	Iso Input 3-	3-	ISO_IN_N3	9	10	ISO_IN_P3	3+	iso Input 3+
	Iso Input 4-	4-	ISO_IN_N4	11	12	ISO_IN_P4	4+	iso Input 4+
#Digital inputs	GND	GND	GND	13	14	GND	GND	GND
	Digital Input 1	I1	GPIN1	15	16	GPIN2	I2	Digtal Input 2
	Digital Input 3	I3	GPIN3	17	18	GPIN4	I4	Digtal Input 4

Pinout 4-20mA IN/OUT

Description	Function	Label	Signal	Pin	Pin	Signal	Label	Function
#4-20mA current loop output	Current Loop Output	O+	OUT +	1	2	GND	GND	GND
#4-20mA current loop inputs	Current Loop Input 2	2+	IN_P2	3	4	IN_P3	3+	Current Loop Input 3
		2-	IN_N2	5	6	IN_N3	3-
	GND	GND	GND	7	8	GND	GND	GND
	Current Loop Input 4	4+	IN_P4	9	10	IN_P1	1+	style="background:#B3B7FF | Current Loop Input 1
		4-	IN_N4	11	12	IN_N1	1-
	GND	GND	GND	13	14	GND	GND	GND

Pinout RTD

Description	Function	Label	Signal	Pin	Pin	Signal	Label	Function
		--	NC	1	2	NC	--
#RTD	RTD 1 (A)	1A	RTD_A1	3	4	RTD_B1	1B	RTD 1 (B)
	RTD 2 (A)	2A	RTD_A2	5	6	RTD_B2	2B	RTD 2 (B)
	RTD 3 (A)	3A	RTD_A3	7	8	RTD_B3	3B	RTD 3 (B)
	RTD 4 (A)	4A	RTD_A4	9	10	RTD_B4	4B	RTD 4 (B)

RS485

An isolated RS485 interface is available as /dev/ttymxc1. The interface includes a switchable termination resistor.

The termination resistor is enabled by driving RS485_TERM_EN high.

Analog inputs

The GW4101 offers connection options for up to four resistive thermal devices (RTD, e.g. PT100/PT1000) and up to four 4-20mA current loop inputs.

Internally an Texas Instruments ADS1220 16-bit ADC ist used. On the Linux side the ADC is accessible via SPI bus.

The cost effective measurement circuit uses a single ADC which is multiplexed to the different measurement channel. To select a channel as well for RTD as also for loop current measurement the channel number (0-3) has to be written to RTDSEL[1..0].

RTD

The following picture shows a simplified schematic of the ratiometric measurement circuit to determine the actual resistive value of the RTD devices.

4-20mA current loop inputs

The measurement of the four loop currents is done one channel at a time by the means of a shunt resistor. The GW4101 provides a per channel current limited (30mA) 24V power supply for easy connection of external sensors.

4-20mA current loop output

The device features a 4-20mA current loop output with integrated loop supply voltage. It is internally realized using a Microchip MCP4716 10-bit ADC with I2C interface.

The following diagram shows the internal architecture of this output.

Digital inputs

The following diagram shows the internal design of the four digital inputs:

This design allows the connection of push-pull- and open-collector-outputs with a threshold of about 4.5V. It is also possible to use a mechanical switch or a relais to connect the input to GND without the need for an additional pullup resistor.

Following diagram shows a simplified design:

Isolated inputs

The following picture shows the simplified architecture one of the four isolated inputs with internal current limit and temperature stabilized threshold. Internally the isolation is achieved by the use of a TLP293 optocoupler.

Isolated outputs

The device contains a Panasonic AQW282 solid state relais to realize two independent isolated outputs. As there is no internal current limitation the user is responsible for ensuring a current flow of max. 300mA.

Linux mapping

Digital and analog I/Os (deprecated sysfs mapping)

Signal	Linux mapping	Typ
ISO_OUT1	/sys/class/gpio178	isolated digital outputs
ISO_OUT2	/sys/class/gpio173
ISO_IN1	/sys/class/gpio176	isolated digital inputs
ISO_IN2	/sys/class/gpio174
ISO_IN3	/sys/class/gpio172
ISO_IN4	/sys/class/gpio177
GPIN1	/sys/class/gpio197	digital inputs
GPIN2	/sys/class/gpio203
GPIN3	/sys/class/gpio194
GPIN4	/sys/class/gpio197	digital inputs
RS485_TERM_EN	/sys/class/gpio175	RS485 termination resisitor
RTDSEL0	/sys/class/gpio205	analog channel select
RTDSEL1	/sys/class/gpio202
ADC_DRDY_n	/sys/class/gpio206	ADC IRQ

Digital and analog I/Os (new libgpiod mapping)

Signal	Linux mapping	line	Typ
ISO_OUT1	gpiochips5	line 18	isolated digital outputs
ISO_OUT2	gpiochip5	line 13
ISO_IN1	gpiochip5	line 16	isolated digital inputs
ISO_IN2	gpiochip5	line 14
ISO_IN3	gpiochip5	line 12
ISO_IN4	gpiochip5	line 17
GPIN1	gpiochip6	line 5	digital inputs
GPIN2	gpiochip6	line 11
GPIN3	gpiochip6	line 2
GPIN4	gpiochip6	line 6
RS485_TERM_EN	gpiochip5	line 15	RS485 termination resisitor
RTDSEL0	gpiochip6	line 13	analog channel select
RTDSEL1	gpiochip6	line 10
ADC_DRDY_n	gpiochip6	line 14	ADC IRQ

Serial interfaces and busses

Interface or bus	Linux mapping
isolated RS485	/dev/ttymxc1
SPI	/dev/spidev2.0	ADS1220
I²C	/dev/i2c-3	MCP4716