Unprogrammable FT232RL on homemade board - Page 1
Forum section: electronics / projects

author: martijnbraam
author_rank: Newbie
timestamp: July 04, 2022, 06:17:21 pm
content: I made a design for a slightly over the top usb to serial converter based around the FT232RL chip. Due to the ship shortage I had this board made by jlcpcb with an HT8232RSZ which should be a fully compatible drop in replacement.The usb-to-serial part of my board works fine but I used the GPIO pins of the chip to drive some shift registers which meant I have to program the EEPROM.When I program the chip using the official ft_prog or with third party tools the software says it's sucessfully programmed but the eeprom contents are not persisted. No errors at all anywhere, the changes are just not persisted. I have tried it with multiple tools and multiple computers . When nothing helped I suspected it might just be a flaw in the HT8232RSZ so I moved an official legit FT232RL from another product to my board expecting that to work so I can start working on the software. Suprisingly it has the exact same issue. I guess this means there's just something wrong with my design but I can't find anything in the datasheets mentioning this or anyone else having this issue.Does anyone have any idea what magic is going on here?Edit: fixed HT8232RSZ part number

author: SiliconWizard
author_rank: Super Contributor
timestamp: July 04, 2022, 06:25:31 pm
content: Quote from: martijnbraam on July 04, 2022, 06:17:21 pmUh sure. I have a hard time finding info on this chip. The only link I found was on LCSC:https://www.lcsc.com/product-detail/RS232-ICs_HTCSEMI-HT232ARZ_C2898743.htmland the attached datasheet is for the HT232A, not a USB-serial interface, but a RS232 transceiver compatible with the MAX232. So, not sure what it's all about. Would you have a link to the part you are talking about?

author: martijnbraam
author_rank: Newbie
timestamp: July 04, 2022, 06:29:54 pm
content: Quote from: SiliconWizard on July 04, 2022, 06:25:31 pmOops I made a mistake and looked up the part on LCSC instead of checking the number in my schematic, it's theHT8232RSZ

author: SiliconWizard
author_rank: Super Contributor
timestamp: July 04, 2022, 07:08:45 pm
content: OK, thanks for the link, and good luck.Beyond this LCSC link, there is almost nothing to be found on the internet (at least that I could.)And judging from the datasheet's content, it kinda looks like the chip is made to use FTDI drivers, and I'd say 50% of the datasheet at least, including schematics, look almost directly copied from FTDI's one.So without further info, I would put this chip in the category of the "clones" that are at least borderline legal. And I'm not utterly surprised if some functionalities do not work as the original. Here, I would even suspect there is actually no internal EEPROM contrary to the FTDI part, which would explain your problem. And it's always interesting to note that those "clones" (at least this one doesn't try to pass as genuine) come with approx. zero support. I suppose you didn't even try contacting the vendor. So any issues the customers may have, the vendor just doesn't care and doesn't even have to get the consequences.Sorry if that sounds like lecturing, I understand that those are hard times and you chose this not to shave off a few cents, but because it was available. So, as I said, good luck!

author: voltsandjolts
author_rank: Unknown
timestamp: July 04, 2022, 07:36:11 pm
content: You say the USB side of things is working (uart functioning), so I would really expect the genuine ftdi internal eeprom programming to work also, since it doesn't depend on any other external connection. My thoughts:(1) Are you sure the 'genuine' ftdi you are using is actually genuine?(2) After programming with ft-prog you need to re-enumerate for new settings to take affect (e.g. unplug form usb and plug in again)(3) Your VCCIO defaults to 1v8 but all other ICs are 5V powered only, including U2 & U3?

author: martijnbraam
author_rank: Newbie
timestamp: July 04, 2022, 09:37:14 pm
content: The FTDI is as genuine as one can ever be sure that's genuine I guess. It's an actual laser etched package that looks like the examples and the eeprom contents actually have a serial number.If it's clone issues then it would be weird if the "genuine" FTDI and the clone have the exact same issue.Quote from: voltsandjolts on July 04, 2022, 07:36:11 pmYep came across that and did that. Doesn't help sadly.Quote from: voltsandjolts on July 04, 2022, 07:36:11 pmI have all the other chips powered form 5V since that should work according to the datasheets. The idea is that I use one of the muxes so I can switch vccio of the whole thing for interfacing with a lot of the random phones I have here.

author: SiliconWizard
author_rank: Super Contributor
timestamp: July 04, 2022, 11:33:10 pm
content: If you're sure the FTDI part is genuine... are you sure you're using FT_Prog properly? Did you make sure you committed the changes?Also, was this genuine part's EEPROM already programmed, or still "blank"? (Thus you'd have the default FTDI parameters?)

author: voltsandjolts
author_rank: Unknown
timestamp: July 05, 2022, 08:52:32 am
content: ^ Hah, yeh, ft_prog ui isn't slick.Quote from: martijnbraam on July 04, 2022, 09:37:14 pmNote that VCCIO is used for the UART pins and the CBUS pins. So you are driving 5V logic level inputs (CLOCK/DATA/LATCH) with 1v8 levels. Maybe this is causing some weirdness that you are interpreting as failure to program the eeprom (setup of CBUS pins) but is actually a hardware problem.

author: shakalnokturn
author_rank: Super Contributor
timestamp: July 05, 2022, 10:47:36 pm
content: A couple of thoughts on the hardware:I haven't looked at VCCIO's current requirements but are you sure U9's internal resistance and no decoupling capacitor on VCCIO is good enough?

author: sicco
author_rank: Regular Contributor
timestamp: July 06, 2022, 07:16:22 pm
content: Detach and then hard wire VCCIO to a hard voltage source that is not first passing a 74HCT4051. Does it then program persistently?Note also that when programming, you may have VSEL0 and VSEL1 both high, and then VCCIO is? Floating. So out of spec.Would a 74HCT4051 really have a low enough Ron? No capacitor on VCCIO?

author: sicco
author_rank: Regular Contributor
timestamp: July 07, 2022, 07:44:43 am
content: Note also that the unused SRCLR input for U6 and U7 is left floating. So not high as you might have assumed. Tie those ‘unused’ inputs to +5.As voltsandjolts already mentioned, driving 5V logic with 1.8V levels may not work. 74ahct595 datasheet states you need >2 volts for a high level. Did you check with a voltmeter that you really do set those 16 bits out of U6,7?I’d expect that if you program VSEL_1 and VSEL_2 both high, that you can never select anything else because VCCIO then will be zero, so clk and data to U6,7 will be 0V for low and 0V for high…The 74hct4051 Ron is 50 ohms typically, but could climb to 200+ ohms when not at 25 C…