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GPIO Design Guide GPIO is a commonly used switch control signal and is widely used in data acquisition and drive control in the industrial field. When GPIO is configured as DI and DO, are the design specifications of dry nodes and wet nodes consistent? When GPIO is configured as DI acquisition, should the isolation solution be relay isolation or optocoupler isolation? 1. What is DI/DO DI: Digital input, converts the digital signal in the production process into the "0" and "1" signal states that are easily recognized by the computer. DO: Digital output, converts the weak digital signal output by the computer into the "0" and "1" signal states that can control the production process. 2. Introduction to DI/DO dry and wet nodes Definition of dry contact: Passive switch, with two states of closed and open. There is no polarity between the two contacts and they can be interchanged. Common dry contacts: limit switch, travel switch, rotary switch, temperature switch, various buttons and output of various sensors, etc. The definition of a wet contact is: an active switch; it has two states: energized and unenergized; there is polarity between the two contacts and they cannot be reversed. Common wet nodes include: the collector output and VCC of an NPN transistor, the collector output and VCC of a Darlington transistor, the output of an infrared reflective sensor and a through-beam sensor, etc. 3. DI/DO drive impedance design Here, NXP i.MX 6UL is taken as an example. When GPIO is used as an output interface, the OVDD voltage is 1.8V or 3.3V. What should be paid attention to when GPIO is designed as DO? Here, DO is taken as an example. Rpu/Rpd and Ztl form a voltage divider, which defines the specific voltage of the incident wave relative to OVDD. The output drive impedance is calculated from this voltage divider. Figure 1 Voltage divider equivalent circuit Figure 3 is based on 3.3V driving impedance table 4. Recommended solutions for designing isolated DI/DO In industrial situations, isolation must be taken into consideration when designing DI/DO. Optocoupler isolation is more commonly used. Figure 4 is an optocoupler isolation digital dry node circuit, in which DIx and GIx are connected to the two ends of the contact switch. When the switch is closed, the optocoupler input circuit diode is turned on, the output circuit photoelectric receiving tube is turned on, and the input end GPIx is low level; when the switch is open, the optocoupler input circuit diode is turned off, the output circuit photoelectric receiving tube is turned off, and the input GPIx is pulled up to a high level by the resistor. Figure 4 Schematic diagram of dry node transmission cable Figure 5 is a reference circuit for the design of optocoupler isolated digital wet node, with an input voltage range of DC4V-18V and built-in filtering function. The user only needs to connect the positive end of the wet node to the DIx interface and the negative end to the GIx interface. When the input voltage is greater than 4V and less than 18V, the optocoupler is turned on; when the input voltage is less than 1V, the optocoupler is turned off. Figure 5 Schematic diagram of optocoupler isolation DI input 1 DI is an isolated digital input interface. When connecting to switch input, the user must add a pull-up power supply to the external circuit. The simplified connection diagram is shown in Figure 6. VCC_GPI is the external isolated power supply with an input range of 4V~18V, GND_GPI is the external isolated ground, and resistor R1 ensures that GIx is at a low level when the switch is disconnected. The resistance value can be 100KΩ. Figure 6 Schematic diagram of optocoupler isolation DI input 2 When DO is used as isolated digital output, the chip provides a DO drive current of mA level and a drive voltage of 1.8V or 3.3V, which cannot meet all application environments. DO is used in the switch quantity design in the industrial field, and needs to be designed with relay isolation, level conversion, and resistor pull-up according to different application environments, which can effectively prevent the reverse injection of voltage signals and burn the chip. Figure 7 Schematic diagram of DO input of isolation circuit Figure 8 M6708U-T series industrial control core board Figure 8 M6708U-T series industrial control core boardFigure 8 M6708U-T series industrial control core boardFigure 8 M6708U-T series industrial control core boardFigure 8 M6708U-T series industrial control core boardpng[/img][/url]Figure 4 Schematic diagram of dry node transmission cable Figure 5 is a reference circuit for the design of optocoupler isolated digital wet node, with an input voltage range of DC4V-18V and an internal filtering function. The user only needs to connect the positive end of the wet node to the DIx interface and the negative end to the GIx interface. When the input voltage is greater than 4V and less than 18V, the optocoupler is turned on; when the input voltage is less than 1V, the optocoupler is cut off. Figure 5 Schematic diagram of optocoupler isolation DI input 1 DI is an isolated digital input interface. When connecting to switch input, the user must add a pull-up power supply to the external circuit. The simplified connection diagram is shown in Figure 6. VCC_GPI is the external isolated power supply with an input range of 4V~18V, GND_GPI is the external isolated ground, and resistor R1 ensures that GIx is at a low level when the switch is disconnected. The resistance value can be 100KΩ. Figure 6 Schematic diagram of optocoupler isolation DI input 2 When DO is used as isolated digital output, the chip provides a DO drive current of mA level and a drive voltage of 1.8V or 3.3V, which cannot meet all application environments. DO is used in the switch quantity design in the industrial field, and needs to be designed with relay isolation, level conversion, and resistor pull-up according to different application environments, which can effectively prevent the reverse injection of voltage signals and burn the chip. Figure 7 Schematic diagram of DO input of isolation circuit Figure 8 M6708U-T series industrial control core board png[/img][/url] Figure 4 Schematic diagram of dry node transmission cable Figure 5 is a reference circuit for the design of optocoupler isolated digital wet node, with an input voltage range of DC4V-18V and an internal filtering function. The user only needs to connect the positive end of the wet node to the DIx interface and the negative end to the GIx interface. When the input voltage is greater than 4V and less than 18V, the optocoupler is turned on; when the input voltage is less than 1V, the optocoupler is cut off. Figure 5 Schematic diagram of optocoupler isolation DI input 1 DI is an isolated digital input interface. When connecting to switch input, the user must add a pull-up power supply to the external circuit. The simplified connection diagram is shown in Figure 6. VCC_GPI is the external isolated power supply with an input range of 4V~18V, GND_GPI is the external isolated ground, and resistor R1 ensures that GIx is at a low level when the switch is disconnected. The resistance value can be 100KΩ. Figure 6 Schematic diagram of optocoupler isolation DI input 2 When DO is used as isolated digital output, the chip provides a DO drive current of mA level and a drive voltage of 1.8V or 3.3V, which cannot meet all application environments. DO is used in the switch quantity design in the industrial field, and needs to be designed with relay isolation, level conversion, and resistor pull-up according to different application environments, which can effectively prevent the reverse injection of voltage signals and burn the chip. Figure 7 Schematic diagram of DO input of isolation circuit Figure 8 M6708U-T series industrial control core board When DO is used as an isolated digital output, the chip internally provides a DO drive current of mA level and a drive voltage of 1.8V or 3.3V, which cannot meet all application environments. DO is used in the switch quantity design in the industrial field. It is necessary to carry out relay isolation, level conversion, and resistor pull-up design according to different application environments, which can effectively prevent the reverse injection of voltage signals and burn the chip. Figure 7 Schematic diagram of DO input of isolation circuit Figure 8 M6708U-T series industrial control core board When DO is used as an isolated digital output, the chip internally provides a DO drive current of mA level and a drive voltage of 1.8V or 3.3V, which cannot meet all application environments. DO is used in the switch quantity design in the industrial field. It is necessary to carry out relay isolation, level conversion, and resistor pull-up design according to different application environments, which can effectively prevent the reverse injection of voltage signals and burn the chip. Figure 7 Schematic diagram of DO input of isolation circuit Figure 8 M6708U-T series industrial control core board
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