RevPi Flat/Flat S

The scope of delivery includes

This power supply requires cabling via the POWER plug.

You will need:

✓ A power supply unit (min. 20 W, e.g. DIN rail switching power supply, article no. 200003)

✓ Wiring, cross section 0.35…2.5 mm

✓ Stripping and crimping pliers

✓ If you use stranded wire, apply suitable wire end sleeves

✓ A small slotted screwdriver

▷ Disconnect connected devices from their respective power supply.

▷ Connect the power supply according to the following pin assignment:

The following parameters, inputs (INP), outputs (OUT) and memory variables (MEM) can be configured:

The RevPi has two RS485 interfaces. This allows you to use serial protocols such as Modbus and to integrate devices such as smart meters or solar inverters into your the Revolution Pi system.

The interfaces are labeled with RS485-0 and RS485-1 . Both interfaces are isolated galvanically from each other and from the RevPi.

Under Linux, the interfaces can be addressed with:

RS485-0 is connected to a 3-pole terminal. The data lines are marked with P (positive) and N (negative). For other devices, these lines are often referred to as D+ and D- or A and B.

Only the lines N and P are required for the actual data transmission. We recommend a twisted pair for longer line lengths or larger baud rates.

An RJ11 socket is available for RS485-1.

Should a reference potential be necessary, you can use the GND electrical circuit ground of the respective RS485 bus for this purpose. Since the two RS485 systems have complete galvanic isolation from each other and from the rest of the RevPi Flat circuitry, these GND connections are also isolated galvanically from each other and from the RevPi Flat GND connection.

Cables having a length over 30 meters and cables leaving the building should be shielded. To further improve the EMC properties of the shield, you can connect the shield to the equipotential bonding rail of the distribution box if necessary. Such a connection can easily be made with a contact force spring.

Linux addresses the interfaces via the character devices /dev/ttyAMA0 and /dev/ttyS0. You can configure bit rates from 50 to 3,000,000 for /dev/ttyAMA0 and from 1,200 to 4,000,000 for /dev/ttyS0. However, occasional reception errors may occur at more than 230,400 bits. The reason is that the UART of the Raspberry Pi, to which the interface is connected, has only a 16 byte FIFO and does not support DMA. The higher the bit rate, the more often the FIFO is not read out fast enough and received data is lost. For example, there are 1 - 2 errors per 50 MByte received at 460,800 bits and there are about 10 errors at 921,600 bits. If your RevPi Flat mainly sends data and only rarely receives it, you can also use higher bit rates. Otherwise we recommend to not set more than 230,400 baud.

✓ The integrated 120 Ω terminating resistor of the RS485 interface is switched off after a restart.

▷ Log in to the RevPi via a terminal.

▷ Check out the Git repository of the command line tool rs485_config from GitLab with the command:

▷ Build the tool with the command:

▷ Activate the resistor with the command:

Replace <SERDEV> with the name of the interface, e.g. /dev/ttyRS485.

▷ Check whether the resistor has been activated and display the settings of the RS485 interface with the command:

❯❯ If the resistor is activated, Bus termination: Yes is output.

The RevPi has two 10/100 Ethernet interfaces with one or three RJ45 sockets for two or four independent MAC addresses. With active autonegotiation, they support half and full duplex.

A transmission rate of 100 MBit/s is available for each interface. All Ethernet interfaces are connected to the internal USB hub. As USB interfaces and Ethernet interfaces share a USB bandwidth, the transfer rate may be reduced if additional USB devices are connected.

The MAC address for LAN 0 is printed on the front of the housing. Under Linux, the interface can be addressed with eth0.

Up to three additional devices can be connected to a network via the three RJ45 sockets for LAN1. They are connected to the internal USB hub via a 1:3 switch. The MAC address for LAN 1 is printed on the front of the housing. Under Linux, the interface can be addressed with eth1.

The three connections for LAN 1 can be assigned to independent MAC addresses via DSA. The storage location for the MAC addresses is /boot/config.txt.

If no addresses are entered in this file or after a new image has been installed, the factory MAC addresses are used.

✓ RevPi base module with WLAN interface

✓ DHCP-enabled WLAN router

▷ Use ip link to check whether a Wi-Fi interface is available.
In Linux, the Wi-Fi interface is displayed as wlan0, provided that no other Wi-Fi device is available.

▷ Activate the WLAN interface via Cockpit^[3].

▷ Set up the WLAN connection via NetworkManager.

A BT interface^[4] is available from standard 5.0.
▷ Activate BT via Cockpit in order to connect Bluetooth peripheral devices such as keyboards or audio devices to the RevPi.

See also:

The RevPi has two USB-A Interfaces. This allows USB 2.0 client devices such as USB hard disks, surf sticks, keyboards or mice to be connected.

the power consumption of the connected devices must not exceed 2.5 W (500 mA @ 5 V) per port. In the event of an overload, the power is switched off at the corresponding USB interface.

The USB interfaces share a USB hub on the RevPi with the two Ethernet interfaces and a Bluetooth interface. This can influence the maximum bandwidth.

The USB interface is suitable for a maximum of 64 DAM-based USB devices.

You can display the USB devices connected to the USB subsystem with the following:

You can use the digital output to switch external devices on and off, for example. It is designed as a potential-free relay contact. Control is therefore effected via a mechanical connection of the pins.

The relay contact may be loaded with a maximum of 30 V DC or 24 V AC and 2 A.

A suppressor diode is connected in parallel to the relay contact to reduce the switching sparks that occur when switching inductive loads. This reduces wear. An external freewheeling diode or similar is not required.

You can switch the relay via piTest with the -w option:

▷ Activate the relay with the command

▷ Deactivate the relay with the command

You can use the gpio program for direct control of the relay via operating system functions. First you must switch the corresponding GPIO - pin — in this case pin 28 — as the output. Then you can set the output with 1 for switch on and 0 for switch off. The example below shows the corresponding sequence of commands:

▷ Set the pin as the output with the command

▷ Switch the output on with the command

▷ Switch the output off with the command

The RevPi has one analog input and one analog output on the 5-pin ANALOG connector.

The analog input can be used to measure either voltage or current.

Current and voltage input must not be connected at the same time, otherwise the measurement result will be distorted.

The current is converted into a proportional voltage via an internal 240 ohm resistor.

The MCP3550-50 analog-to-digital converter (ADC) used for this purpose offers a high usable resolution of 21 bits, but at 85 milliseconds per measurement, it requires a comparatively long time.

There are two ways to access the interfaces: either by reading and writing the Linux sysfs or by using our RevPi configuration tool PiCtory and the software tool piTest, which allows you to access the process image of the system. In the following we describe both methods separately for input and output.

Read out voltage 0 … 10 V:

▷ Obtain the input value of the ADC with:

▷ Convert the raw value read out to in_voltage0-voltage1_raw with the formula ($raw * 12500) >> 20) + 12500 to obtain the voltage in mV.

Read out current 0 … 20 mA:

✓ The current should be on the port I IN: are available.

▷ Divide the read out voltage (see above) by a resistance of 240 ohms to obtain the current in mA.

You can configure the current/voltage mode for the RevPi Flat in PiCtory with the variables AInMode :

▷ Simply read out the current or voltage value by entering

You can connect actuators such as frequency converters to the analog output. It can output a voltage between 0 and 10 V.

The DAC121S101 digital-to-analog converter (DAC) used for this purpose has a resolution of 12 bits.

▷ Enter the value in the DAC with:

▷ Enter a value between 0 and 4095 into the DAC out_voltage0_raw to output a voltage between 0 and 10 V.

▷ Enter the analog value in mV in the variable AOut e.g. 5000 mV for the analog output:

On the software side, the DAC121S101 and MCP3550-50 are treated like I/O modules whose interface is implemented in sysf as /sys/bus/iio/devices/.

After the converters are successfully registered, the following kernel log usually appears.

Two subfolders are added to the folder sysfs for the converters as /sys/bus/iio/devices/iio:deviceX. You can use × to distinguish between the converters here. The order depends on the registration of the devices and therefore has no fixed assignment. The assignment becomes apparent, however, when you look at the contents of the folders. The folder with the files out_voltage is the output module and therefore the DAC module. The folder with the files in_voltage is the input module and therefore the ADC module.

In the method with piTest, piControl retains these values permanently in the process image and you can read and write the values with piTest.

See also:

The RevPi is equipped with the Trusted Platform Module Infineon OPTIGA™ TPM SLB 9670. It fulfills the requirements of TPM 2.0.

Under Linux you can address the module with /dev/tpm0.

The RevPi has two independent watchdogs. The first is part of the BCM2837 SoC, which is also used on the Raspberry Pi 3. The second is the Maxim MAX6370 external watchdog module.

The BCM2837 watchdog is the preferred watchdog because it behaves like other watchdogs under Linux. You can access it either via the device file /dev/watchdog0 or as a default watchdog via the device file /dev/watchdog.

The MAX6370 can be accessed via the device file /dev/watchdog1.

To activate it, GPIO4 must be set high once. It can no longer be deactivated via this GPIO, however. For activation via the command line, you can use the gpiod tool:

The command gpioset is part of the gpiod package. If this is not installed, you can install it yourself with:

If you want to operate the GPIO from your application, the libgpiod is right for you. This also provides a Python interface.

You will need the following packages:

The timeout of the MAX6370 is fixed at 60 seconds and cannot be changed.

Once activated, the Watchdogs MAX6370 can only be deactivated by disconnecting the power supply. A restart does not deactivate the watchdog. This means that a restart must not take longer than 60 seconds when the watchdog is active, otherwise the hardware will be reset.

There are several ways to use a watchdog under Linux. Revolution Pi and Raspbian Pi rely on systemd. This is therefore also the preferred method of using the watchdog. systemd can be used to trigger a hardware watchdog. Applications that are to be monitored by the watchdog are then monitored by systemd. This has the advantage that several applications can be monitored. Consequently, the entire system does not necessarily have to be restarted, but instead only the individual application.

See also:

The RevPi has a freely configurable button. The input value of the button can be evaluated via GPIO13 and then used for certain actions, e.g. for a controlled shutdown of the RevPi.

In the PiCtory Value Editor, the input value of the push-button is entered under Top_Button displayed.

It can be retrieved by software in the same way as a keyboard entry. The KEY_UNKNOWN key code is used (corresponds to value 240).