FTDI Chip Gone Wild

Kye

Hey guys,

I just finished building a prototype on the prop protoboard, and I'm having a bit of problems with the FTDI chip now. I connected a max232 to the serial line for serial port communication. The send and receive lines are configured properly for the·propeller chip and I'm not having any problems with the propeller chip, but the FTDI chip is another question.

When the usb cable is not attached to the FTDI chip the·red LED(near the usb port)·(which I think is the receiveing indicator·flashes really fast and then stays lit (because it may be flashing even faster)).

I think it may have been caused by the max232 as I used 5v for vdd on the max232. So I may have damaged the FTDI chip. So after I thought of this I removed the max232 from its socket.

Now, after removing the max232 chip the red LED (near the usb port) flashes very dimly about every second when the usb cable is not attached. The only other things on the lines are two·LEDs (which I installed)·with pull up resistors that flash when the lines·are pulled down (the resistors are 100 ohm and connected to the 3.3v source).

Also an 100 ohm·resistors·are in series with the send and receive lines to prevent damage to the propeller, and the FTDI chip.

So, did I break the FTDI chip?

And if so then why does it fix itself with usb power? And why isn't the propeller chip damaged then?

Thanks,

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Nyamekye,

Phil Pilgrim (PhiPi)

Kye,

Several things come to mind here:

1. You should definitely be using a MAX3232 powered from 3.3V, not a MAX232.

2. If you're using both serial lines, the logic-side output of the MAX232/3232 will be driving the output pin of the FT232R, which is never good, even when the FT232R is not powered from the USB port.

3. There is a known problem with Parallax's FT232R/Propeller interface design, by which output from the Propeller can power the FT232R through its input pin. This usually results in the Propeller chip being reset when the FT232R's DTR output triggers the transistor driving the /RST line.

Why not just connect a MAX3232 chip to something other than the lines shared by the FTDI chip? Otherwise, I would recommend cutting the trace from the FT232R's TxD line and attaching a three-pin header, so you can select which chip is driving the Prop. To address #3 above, you can also connect a 1K pullup to the FT232R's RXD line.

-Phil

Kye

Ah so thats why that happens....

I also changed it to a 3232 and it works (except for a few errors here and there... mostlikely from the ft232r)

Um, how would I cut the trace and attach a hearer? Theres no real space for that.

But would just attaching pull ups fix the problems, and maybe increasing the series reistance?

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Nyamekye,

Phil Pilgrim (PhiPi)

You're still going to have a bus conflict on the FT232R's TxD pin if you also connect it to an output from the MAX3232. My recommendation would be to use different port pins if you're not able to get access to that trace to cut it and install a 3-pin header.

-Phil