Maxx GW4100

The Device

Linux login

Per default login to the Linux system is possible by the use of a ssh connection on eth0 or via the serial console on the RS232 interface (115.200 baud, 8N1).

login: root

password: root

Please be advised to at least change the password and deactivate the serial console before deploying the device. The use of further security measures (PSK etc.) is strongly encouraged.

Interfaces

The following section describes the various interfaces of the GW4100 in detail. This graphic shows the distribution of the interfaces:

((ABB))

Power

The device requires an external ES1/PS2 DC power supply 8-30V, 25W.

Ethernet

10/100MBit ethernet interface, per default configured as DHCP server with IP address 192.168.1.1.

USB

USB 2.0 host interface for connection of external USB devices. Please note that an appropriate Linux driver ist required for many devices.

SD card

Micro SD card interface for adding additional non-volatile memory to the system. Please use a SD card to store rapidly changing data (e.g. databases etc.) as the internal flash memory allows limited write cycles before potential memory corruption may occur.

CAN

The interface according to the CAN 2.0B protocol specification is relaized using the i.MX7D’s flexcan interface and a NXP TJA1051 transceiver. It features a switchable 120R termination resistor.

On the Linux side a SocketCAN interface (can0) with a default bitrate of 250.000 bit/s is provided.

The termination resistor is activated by driving CAN_TERM_EN_n low. See Linux mapping for details.

RS485

A non-isolated RS485 interface is available as /dev/ttymxc3. The interface does not include a termination resistor.

RS232

A 4-wire RS232 interface is available as /dev/ttymxc2. In default configuration this interface will provide a Linux serial console at 115200 baud (8N1).

1-wire

The GW4100 incorporates a DS2482 I2C to 1-wire bridge device from Maxim Integrated (https://www.maximintegrated.com/en/products/interface/controllers-expanders/DS2482-100.html#). The corresponding driver is integrated in the Linux mainline kernel and all 1-wire functions are exposed to the sysfs filesystem.

Please see https://www.kernel.org/doc/html/latest/w1/w1-generic.html for a detailed description of the user space interface.

Digital inputs

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

((ABB))

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:

((ABB))

Please note that the input is inverted internally so that in case the input is either unconnected or connected to a voltage above the threshold will be read as logical 0 (low level), when connected to a voltage below the threshold (e.g. 0V) it will be read as logical 1 (high level)

The GPIs are exposed to the sysfs filesystem on the linux side an can be automatically inverted again for user conveniance.

TODO: add linux example

Multi-purpose I/O

The device contains two multi-purpose GPIOs which can be configured as in- or output. When required an internal pullup resistor can be activated.

Furthermore can the GPIO be used as an analog input as the input voltage is also connected to one of the internal 12-bit ADC channels (s. On board ADCs) .

((ABB))

The GPIO is current limited (tbd mA) in the high- and lowside current paths so closing high- and lowside switches at the same time will not damage the device (neither will an external short-circuit condition), it is nevertheless not advised to do so and use break-before-make logic instead.

TODO: add linux example