The data manual lists the default state of the pins at power up. That is the first thing I would look at as there is nothing you can do to change those..Be careful on the LCD pins as those are also the boot pins.
http://www.ti.com/product/am3359 After that, you can change the default setting from the SW by crating your own DTS file. Gerald On Mon, Jan 27, 2014 at 8:40 AM, <[email protected]> wrote: > So after I had a nice PCB all laid out and routed I was looking at some of > the GPIO I was planning to use with a voltmeter and noticed I had a lot of > problems. These problems took the form of some GPIO being pulled up or > down at power-up in opposition to the control signals I was planning. > > 1.) One case was P9_15 where the bootup condition is 1.6V???? That would > hold my signal right smack in no-mans-land between high and low. Looking > at the schematic I see that pin is in tug-of-war with another one that is > not on the headers so I don't understand the intention there. > > 2.) In another case the pin I selected was pulled low which means I would > be putting invalid data on an output buffer because the /OE line is pulled > low at power on unless my external pull-up was extremely strong. > > 3.) The worst case I found however, was the LCD control signals shared > with GPIO (P8_27 - P8_30). LCD_DE and LCD_HSYNC are both driven low at > boot and my design originally had those setup as BBB Inputs that would be > fed from an external buffer. The moment that /SYS_RESETn went high, those > buffers would be enabled and driving their outputs as well. If there is a > conflict then I have a clear contention issue that could zap one or the > other part. I discovered this when connecting those pins to a pull-up had > no effect on the output voltage. Where they simply pulled low then my > pull-up would have created a voltage divider and raised the voltage at that > pin. > > Is there anything that lists the pins and the default logic state that's > on them when the device boots? I also didn't see anything that mentioned > the SRM about being wary of LCD_HSYNC and LCD_DE being driven low. I > looked at the schematic and there is a resistor shown on each of those > signals but no indication of the value. Is that to protect from > contention? If the HDMI framer is disabled should/will those pins remain > driven? > > -- > For more options, visit http://beagleboard.org/discuss > --- > You received this message because you are subscribed to the Google Groups > "BeagleBoard" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > For more options, visit https://groups.google.com/groups/opt_out. > -- For more options, visit http://beagleboard.org/discuss --- You received this message because you are subscribed to the Google Groups "BeagleBoard" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/groups/opt_out.
