> I'm trying to go a bit beyond a basic breakout... I want to make a
> board with an interface to my LCD (sony), 3 Serial ports, 4 buttons, and
> 12v power supply. I have a few questions:
> 1) Do I need to hold any specific pins high or low on the gumstix? I'm
> routing all of the serial port pins to actual serial ports (through
> level converters) so I think thats taken care of. I see the NRESET pin
> which I assuming is Not Reset so I'm assuming I want to hold that high.
> Do I need to delay bringing this up for any amount of time ot get the
> clock to stabailize as mentioned in the PXA manual?
If you take a look at the breakout-gs schematic, it only connects a few
pins. The Y0_RXD is pulled up, Y0_RTS & Y0_CTS are used as part of the USB
connection but could otherwise be unconnected.
Other than that, I don't think that there's anything else that have to hook
> 2) For the buttons on the GPIO pins (I'm stealing the JTAG pins) do I
> need to hold / bring them high or low? I just don't want to duplicate
> anything thats already done.
Only the old boards have JTAG pins and the JTAG pins aren't shared with GPIO
lines so you can't use them for buttons.
> Looks like I should hold them low with a 470k resistor and bring them
> high with a 1.5K resitor to VCC???
Huh. For buttons, I'd use something big (10K-47K) as pullups and just have
the resistors pull to ground. If you want current limiting protection
(because the GPIO line is configured as output) then stick a 100 ohm
resistor inline between the button and ground.
> 4) Do I understand the USB interface correctly?
> GPIOn is designed to tell the Gumstix that the cable is connected but
> needs to be dropped to 3.3v?
The MAX823 chip also acts a debounce circuit so you don't get multiple hits
on the GPIO line. Otherwise you'd get a bunch of edges when you insert the
> GPIOx is left floating (as input), when connect is detected, this drives
> high to say this is a high speed device?
When a connection is desired, pulling D+ high tells the host that a device
is present. Otherwise the host thinks that the cable is unconnected.
And, yeah I believe it also tells the host that its a full speed device
(full speed is 12 Mbps, high speed is 480 Mbps - this definitely isn't high
Vancouver, BC, Canada
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