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Protocol The protocol supports communication via inputs/outputs of Raspberry PI and computers built on a an RPI Compute Module. Currently supported are:
- Raspberry PI (version 2, 3, and 34) based on a pigpio library - communication via GPIO (General Purpose I/O) pins
- Techbase NPE X500 M3 (DIN-mounted industrial computer built on RPI Compute Module 3 with industrial inputs and outputs)
The communication was tested with Raspberry PI (version 3) and NPE X500-M3-MAX-3G.
For Raspberry PI, the protocol protocol supports reading of digital inputs (instantaneous values as well as counting signal changes with an optional time filter) and setting digital outputs to a constant value or pulse-width modulation (PWM).
For NPE X500 the protocol supports protocol supports reading of digital and analog inputs and status of user button, writing to digital outputs, setting relay outputs, working with user LEDs, and a buzzer.
Note: On Raspberry PI, the KOM process must be run under the root user to gain access to the GPIO. It is possible to achieve by setting the setuid bit for the kom binary. Under the user pi, you can do the following:
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Communication line - configuration dialog box - the Protocol parameter tab.
Parameters defined in the field have an effect on some optional protocol parameters. There can be defined the The following line protocol parameters can be defined:
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| Full name | Description | Units / size | Default value | ||||||
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| Type of device. Currently supported are::
| - | Raspberry PI | ||||||
| Name of the library with communication functions for a particular device. The used values are:
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| Delay after one reading of the values of all I/O tags. Using this parameter, it is possible to control the reading frequency more finely than using the polling parameters in the configuration of the time parameters of the station. | ms | 1 |
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| Address | Description | I/O tag type | Examples |
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DI,id | The GPIO pin will be configured as a digital input. If the voltage of 3.3V is applied to it, the value of input will be 1. If 0V (ground) voltage is applied to it, the value of input will be 0. | Di, Ci, Ai | DI,25 DI_UP,24 |
DO,id | The GPIO pin will be configured as a digital output. If a value of 1 is written to it, the output will be 3.3V. If 0 is written, the output voltage will be 0V (ground). | Dout, Co, Ao | DO,24 |
| TRIGGER_TOON,id[,filter] TRIGGER_TOON_UP,id[,filter] TRIGGER_TOON_DOWN,id[,filter] TRIGGER_TOOFF,id[,filter] TRIGGER_TOOFF_UP,id[,filter] TRIGGER_TOOFF_DOWN,id[,filter] TRIGGER,id[,filter] TRIGGER_UP,id[,filter] TRIGGER_DOWN,id[,filter] | The GPIO pin will be configured as an a counter of input events with an optional filter. The counter can register rising signal edges 0V → 3.3V (TOON), falling edges 3.3V → 0V (TOOFF), and any signal changes (without TOON/TOOFF). | Ci, Ai | TRIGGER,24 |
| PWM,id | The GPIO pin will be configured as PWM (pulse width modulation) output. It is then possible to write values 0-255 controlling the width of the pulse from fully off to fully on. | Dout, Co, Ao | PWM,12 |
| REVISON | The revision of the hardware (the number from the "Revision" line from the /proc/cpuinfo file. For example, for RPI 3 this file contains a row | Ci | REVISON |
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In the following table, id defines the number of input/output (e.g. DI, DO, AO). The number of inputs and outputs depends on the particular model. The notes are referring to the NPE X500-M3-MAX-3G that was tested.
Note 1: Output points whose addresses contain _BUF use a buffered writing. This allows the values of such objects not only to be written , but also to be read, which can be useful, for example, after the start of the KOM process.
Note 2: With the tested model, the reading of the digital input took less than 1 ms, while the reading of the analog input took approximately 20 ms.
| Address | Description | I/O tag type | Examples |
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DI,id | Digital input (DI) | Di, Ci, Ai | DI,1 DI,2 |
DO,id | Digital output (DO). If buffered (DO_BUFF), the value is also read (during startup and periodically). | Dout, Co, Ao | DO,1 |
| DIO,id DIO_BUF,id | Digital input/output. Based on the I/O tag type, the GPIO port is configured as input (Di, Ci, Ai) or output (Dout, Co, Ao). | Input: Di, Ci, Ai Output: Dout, Co, Ao | DIO,2 DIO_BUF,3 |
| RELAY,id RELAY_BUF,id | Relay output. If buffered (RELAY_BUFF), the value is also read (during startup and periodically). | Dout, Co, Ao | RELAY,1 RELAY_BUF,2 |
| AI,id | Analog input (AI). | Ci, Ai | AI,1 |
| LED,id LED_BUF,id | LED output. If buffered (LED_BUFF), the value is also read (during startup and periodically). | Dout, Co, Ao | LED,1 LED_BUF,2 |
| BUZZER BUZZER_BUF | Buzzer. If buffered (BUZZER_BUFF), buzzer status is also read (during startup and periodically). | Dout, Co, Ao | BUZZER BUZZER_BUF |
| BUTTON BUTTON_BUF | User button status. | Di, Ci, Ai | BUTTON |
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You can read a blog about GPIO protocol: GPIO protocol is here to help |
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