Hi there !
I noticed that the documentation for the FT232 backpack says, it can be used as FT232 breakout :
http://dangerousprototypes.com/docs/USB ... D_backpack (http://dangerousprototypes.com/docs/USB_Universal_LCD_backpack)
The problem is that RXD input is driven by a shift register output, and there seems to be no way to disable it.
Do I have to desolder the shift registers to use the PCB as FT232 breakout, or is there a smarter way to do it ?
Thank you in advance
Two ideas...
1) Just cut the trace from the second shift register leading into the FT232. There is no compelling reason for it to be there - why would the computer need to receive the data that it just sent previously?
2) Make the FT232 set its DSR output a high level. This will disable the outputs of the shiftregisters and they will be in high impedance mode so they can't affect the RXD pin of the FT232.
You're right, those shift registers are output only, so there no use in reading data back.
I thought about your 2) solution, but sadly DSR disables only parallel outputs of the shift registers, and RXD is driven by the "serial output" pin, which doesn't have a high impedence mode. Moreover I'd like to be able to use the DSR signal as I wish.
So I think I will go with your first solution and cut the serial output trace.
Thank you !
[quote author="Grapsus"]I thought about your 2) solution, but sadly DSR disables only parallel outputs of the shift registers, and RXD is driven by the "serial output" pin, which doesn't have a high impedence mode. ![/quote]
That's true, and it makes sense that the SerialOut-pin would not go into HiZ because that would leave the SerialIn-pin on the next unit in a daisy chain with an undefined level.....