I am trying to understand the use for each pin on the Extension Header (x27). More specifically pins 1-12. The difference between pin 25 compared to 22-24. Finally pins 33-35 from my understanding this is to control backlights, I guess I’m not sure in which application would you need multiple unless you’re powering multiple displays.
Hi, I’m the Toradex AI Assistant.
I might make mistakes. Our support team will step in if needed. If I answered your question, please tick the “Solution” checkbox. For follow-up questions to me, please use @ToradexAI in your post.
Did you like my answer? 
Extension Header (X27) Pin Functions
Based on the Ixora V1.3 datasheet, here’s the breakdown of the Extension Header (X27) pins you asked about:
Pins 1-12: System Control and Communication
These pins provide essential system control and communication interfaces (1):
- Pins 1-4: System control signals including RESET_MICO#, POWER_ENABLE_MOCI, WAKE1_MICO#, and RESET_MOCI# (1)
- Pins 5-6: I2C1 interface (SDA and SCL) with 1.8K pull-ups to 3.3V_SW (1)
- Pin 7: Ground (1)
- Pins 8-11: SPI1 interface (CLK, CS, MISO, MOSI) (1)
- Pin 12: 5V_SW power supply (1)
Pin 25 vs Pins 22-24: Different Voltage References
The key difference is the voltage reference (1):
- Pins 22-24: AN1_ADC0, AN1_ADC1, AN1_ADC2 - These are analog inputs referenced to +3.3V (1)
- Pin 25: AN1_TSWIP_ADC3 - This is also an analog input referenced to +3.3V, but it’s specifically designated for touchscreen functionality (TSWIP = Touch Screen Wire Interface Protocol) (1)
All these pins have the same +3.3V voltage reference, but pin 25 has specialized touchscreen functionality.
Pins 33-36: PWM Outputs (Not Just Backlight Control)
These are general-purpose PWM outputs (1):
While PWM signals are commonly used for backlight control, these pins serve multiple purposes beyond just displays. Applications include:
- Multiple Display Backlights: As you mentioned, for systems with multiple displays
- Motor Control: PWM signals for controlling motor speed and direction
- LED Brightness Control: For status LEDs or general lighting
- Audio Generation: Simple tone generation
- Servo Control: For robotics applications
The PWM_A signal is specifically routed to the RGB display connector (X7) to provide backlight brightness control for connected LCD displays, which is why a populated zero ohm resistor (R15) has been placed before connector X9 (2).
Best regards, Toradex AI Assistant.
What are some common uses for the system control signals, I2C1Interface, & SPI1 interface?
The meanings of control signals such as RESET_MICO#, POWER_ENABLE_MOCI, WAKE1_MICO#, RESET_MOCI#, etc., are described in the respective module datasheets (e.g., Apalis iMX6 Datasheet, Apalis iMX8 Datasheet) and in the Apalis Carrier Board Design Guide.
The I2C and SPI interfaces are both used for short-distance, on-board communication in embedded systems, connecting a central processor to various peripheral devices. The choice between them depends on the application’s specific requirements for speed, wiring complexity, and the number of devices on the bus
1 Like