Need help with FT232RL

[aruna1]

Hi
I recently designed a USB relay controller, and I have the prototype boards in my hand.

USB communication was intended to achieve through famous FT232RL chip.

I have soldered the MCU and FT232 and found out it is not working.

then I tried to see if FT232 is working properly by connecting RX to TX and doing echo test. test was a fail

Then I connected my logic analyzer to TX pin (pin 1) of FT232 and tried to capture its output while sending serial characters through USB.

according to the logic analyzer , output of FT232 is incorrect.

it lowers its output for the full length of the character and then set to high. this is same with any character.

then I tried changing chips but ended up with same result.

I have attached analyzer output and the schematic here.

Is there anything I'm doing wrong here? (this is my first time with FT232) any configurations needed?
or am I a victim of counterfiet ICs? (brought FT232 from chinese seller) (but FT_PROG can read and write FT232 chips EEPROM)

(LEDs are connected incorrectly, i noticed it after production of prototype boards. but I dont think that is the reason for this coz I checked the output after removing those LEDs)




Thanks

[PA0PBZ]

The only thing I see missing is the 100nF cap on pin 17, but since that seems to be only for the USB interface and you can read the EEPROM it's unlikely that it's your problem.
When you look at the timing of the TX pin signal, is it equal to 10 bits?

[nctnico]

You can leave the reset pin open. Perhaps its not intended to be connected to VCC at all.

[PA0PBZ]

From the datasheet:

"Active low reset pin. This can be used by an external device to reset the FT232R. If not required can be left unconnected, or pulled up to VCC."

[nctnico]

'pulled up' is something different than 'connected to'. The rest of the circuit looks the same as a circuit I'm using so the reset pin might be a good place to start.

[David_AVD]

What are you using to send the data for the echo test?

[aruna1]

The only thing I see missing is the 100nF cap on pin 17, but since that seems to be only for the USB interface and you can read the EEPROM it's unlikely that it's your problem.
When you look at the timing of the TX pin signal, is it equal to 10 bits?

I connected external cap to pin 17 and tried but  result is same.
I'm not sure about 10bits thing. it seems to be only 8 sample points (in logic analyzer image)

You can leave the reset pin open. Perhaps its not intended to be connected to VCC at all.

From the datasheet:

"Active low reset pin. This can be used by an external device to reset the FT232R. If not required can be left unconnected, or pulled up to VCC."

'pulled up' is something different than 'connected to'. The rest of the circuit looks the same as a circuit I'm using so the reset pin might be a good place to start.

I will try pulling up the reset line. will post result here

What are you using to send the data for the echo test?

I used secureCRT terminal software

[Psi]

Perhaps it was pre-programmed with some weird settings from factory (Chinese sellers often sell left over production runs)
I would go through with FT_PROG and confirm all settings are at default.

Also try a different PC, just in case the PC you're using is running some weird FTDI driver. (Lots of other products use the same chip and may have installed their own driver which is taking preference)

[aruna1]

Perhaps it was pre-programmed with some weird settings from factory (Chinese sellers often sell left over production runs)
I would go through with FT_PROG and confirm all settings are at default.

Also try a different PC, just in case the PC you're using is running some weird FTDI driver. (Lots of other products use the same chip and may have installed their own driver which is taking preference)

how can i get correct settings?

[aruna1]

I tried after disconnecting "reset" pin from vcc and left it unconnected. but result is the same.

any suggestions?

[David_AVD]

Do you have another FT232RL based serial dongle that you can try the loopback test with?

Maybe a picture of the setup will help?

[vl400]

I cant view the schematic for some reason, have you got the test pin grounded?

[David_AVD]

Did you do the loop back test by connecting Rx and TX on the actual FT232 chip, or via the opto couplers ?

[aruna1]

Did you do the loop back test by connecting Rx and TX on the actual FT232 chip, or via the opto couplers ?

I loop back tested directly via ft232 RX TX pins.

I cant view the schematic for some reason, have you got the test pin grounded?

yes, test pin is grounded

Do you have another FT232RL based serial dongle that you can try the loopback test with?

Maybe a picture of the setup will help?

here i have posted a image of FT232 layout. sorry I cannotpost entire design

[David_AVD]

Apart from the missing capacitor (pin 17) the board looks ok.  How did you miss that capacitor anyway?  It's shown in the data sheet examples.

Time to go buy a replacement chip from a reputable source I think.  Otherwise you'll never know if it's the chip (batch) or not.

[aruna1]

Apart from the missing capacitor (pin 17) the board looks ok.  How did you miss that capacitor anyway?  It's shown in the data sheet examples.

Time to go buy a replacement chip from a reputable source I think.  Otherwise you'll never know if it's the chip (batch) or not.

this is my first time making a prototype PCB through fab house. so I guess I was careless about capacitor.

I have already ordered another chip from other place. should arrive tomorrow

[aruna1]

Problem solved.
I brought 2 FT232RL from another source and they worked perfectly.
It seems all FT232 ics I brought before are damaged products.

Thanks everybody for the help