I’m working with the following hardware:
Colibri T20 512 V1.2A with WEC 7, Viola Plus board V1.2B, Colibri Eval. board V3.2B
and attempting to get an LCD screen working.
Using the Colibri and Viola board, with a screen connected to the UDI flat flex connector, the screen isn’t working properly. I’ve tracked the problem down to the LCD_BIAS signal (SODIMM 44). If I probe that signal (pin 32 of X7 on the Viola), I see no activity. If I use the GPIO Config tool within Windows CE, I can’t even set the level of the pin as a GPIO.
However, if I move the same Colibri module, without making any changes, to the Colibri Eval. board, boot to the CE desktop, and probe SODIMM 44 on connector X9, the LDC_BIAS signal is doing what it should be doing. I can also control the pin through the GPIO Config tool as expected.
I don’t understand what’s causing this pin to work properly on the Eval. board, but not on the Viola board, using the very same Colibri module.
Is there any known reason this could be happening?
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Based on the context provided, there isn’t specific information about the behavior of the LCD_BIAS signal on the Viola board with the Colibri T20 module. However, I can provide some general troubleshooting steps and considerations that might help you identify the issue:
Pin Multiplexing and Configuration: Ensure that the pin multiplexing and configuration for the LCD_BIAS signal (SODIMM 44) are correctly set up in the software. The Viola board might have different default configurations compared to the Colibri Eval board.
Hardware Differences: Check if there are any hardware differences between the Viola board and the Colibri Eval board that might affect the LCD_BIAS signal. This could include differences in pull-up/pull-down resistors, level shifters, or other components that might influence the signal.
Power Supply and Initialization: Verify that the power supply and initialization sequence for the LCD and related signals are correctly implemented on the Viola board. Sometimes, power sequencing issues can cause certain signals to not behave as expected.
Software Configuration: Ensure that the software configuration (e.g., registry settings in Windows CE) is correctly set up for the Viola board. There might be board-specific settings that need to be adjusted.
Signal Integrity: Check for any signal integrity issues on the Viola board. Poor connections, damaged traces, or other physical issues could cause the signal to not function correctly.
Documentation and Support: Refer to the Viola board and Colibri T20 module documentation for any notes or errata related to the LCD_BIAS signal. Additionally, you can contact Toradex support (support@toradex.com) or post a question on the Toradex community forum for more specific assistance.
If these steps do not resolve the issue, it might be necessary to perform a more detailed investigation with the help of Toradex support.
On the Viola board, the LCD_BIAS signal (SODIMM 44) is directly routed to pin 32 of the X7 connector, with no other electrical components involved. Therefore, the only reason I can imagine for the behavior you described is a damaged FCC cable or connector causing that pin to be pulled up or down.
Please also note that SODIMM 44 on the Colibri T20 module is multiplexed—two Tegra SOC balls (L_BIAS and LCD_M1) are connected together.
Thanks a lot for the quick response. It did turn out to be a bad connector on the screen hardware.
On the subject of the multiplexed pins, I didn’t find any documentation on what the LCD_M1 signal is. The L_BIAS signal seems to work fine under the display driver’s control, so there’s no issue to resolve, but does LCD_M1 have a specific function that’s different than L_BIAS?
“Details about the LCD_M1 and L_BIAS pin functionality can be found in the Tegra 2 Technical Reference Manual. By default, Colibri T20 X1 pin 44 acts as the Data Enable signal for active displays and parallel RGB to VGA or LVDS converters. For passive displays, you can use this pin as the Bias/Modulation pin.”
