Need help with FT232RL - Page 1
Forum section: electronics / projects

author: aruna1
author_rank: Regular Contributor
timestamp: May 08, 2013, 05:41:01 pm
content: HiI 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 failThen 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

author: PA0PBZ
author_rank: Super Contributor
timestamp: May 08, 2013, 07:11:28 pm
content: 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?

author: nctnico
author_rank: Super Contributor
timestamp: May 08, 2013, 08:27:05 pm
content: You can leave the reset pin open. Perhaps its not intended to be connected to VCC at all.

author: PA0PBZ
author_rank: Super Contributor
timestamp: May 08, 2013, 08:47:23 pm
content: 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."

author: nctnico
author_rank: Super Contributor
timestamp: May 08, 2013, 09:03:25 pm
content: '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.

author: David_AVD
author_rank: Super Contributor
timestamp: May 08, 2013, 09:34:14 pm
content: What are you using to send the data for the echo test?

author: aruna1
author_rank: Regular Contributor
timestamp: May 08, 2013, 11:45:35 pm
content: Quote from: PA0PBZ on May 08, 2013, 07:11:28 pmI 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)Quote from: nctnico on May 08, 2013, 08:27:05 pmQuote from: PA0PBZ on May 08, 2013, 08:47:23 pmQuote from: nctnico on May 08, 2013, 09:03:25 pmI will try pulling up the reset line. will post result hereQuote from: David_AVD on May 08, 2013, 09:34:14 pmI used secureCRT terminal software

author: Psi
author_rank: Super Contributor
timestamp: May 08, 2013, 11:46:03 pm
content: 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)

author: aruna1
author_rank: Regular Contributor
timestamp: May 08, 2013, 11:52:19 pm
content: Quote from: Psi on May 08, 2013, 11:46:03 pmhow can i get correct settings?

author: aruna1
author_rank: Regular Contributor
timestamp: May 09, 2013, 05:09:50 am
content: I tried after disconnecting "reset" pin from vcc and left it unconnected. but result is the same.any suggestions?

author: David_AVD
author_rank: Super Contributor
timestamp: May 09, 2013, 05:15:21 am
content: Do you have another FT232RL based serial dongle that you can try the loopback test with?Maybe a picture of the setup will help?

author: vl400
author_rank: Regular Contributor
timestamp: May 09, 2013, 06:54:54 am
content: I cant view the schematic for some reason, have you got the test pin grounded?

author: David_AVD
author_rank: Super Contributor
timestamp: May 09, 2013, 08:17:34 am
content: Did you do the loop back test by connecting Rx and TX on the actual FT232 chip, or via the opto couplers ?

author: aruna1
author_rank: Regular Contributor
timestamp: May 09, 2013, 03:16:26 pm
content: Quote from: David_AVD on May 09, 2013, 08:17:34 amI loop back tested directly via ft232 RX TX pins.Quote from: vl400 on May 09, 2013, 06:54:54 amyes, test pin is groundedQuote from: David_AVD on May 09, 2013, 05:15:21 amhere i have posted a image of FT232 layout. sorry I cannotpost entire design

author: David_AVD
author_rank: Super Contributor
timestamp: May 09, 2013, 09:10:08 pm
content: 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.

author: aruna1
author_rank: Regular Contributor
timestamp: May 10, 2013, 12:20:30 am
content: Quote from: David_AVD on May 09, 2013, 09:10:08 pmthis 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

author: aruna1
author_rank: Regular Contributor
timestamp: May 12, 2013, 07:25:40 am
content: 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