FTDI USB-RS485 Plus 2: Unable to set to 10MBaud from Window - Page 1
Forum section: electronics / projects

author: riscy00
author_rank: Contributor
timestamp: July 14, 2023, 05:56:58 pm
content: Is there way for Window or FTDI to set to 10MBaud. I tried that and measure on scope probe and it well below 10MBAUD. Tested good for 5M, 8M but fails at 9M and 10M. The datasheet say it goes up to 10MBaud.Open for idea.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: July 14, 2023, 08:25:33 pm
content: Quote from: riscy00 on July 14, 2023, 05:56:58 pmWhich FTDI part ? No data I can find says 10M (or 5M) - on the FT2232H/FT232H the supported BAUD is24MHz/Nso you need to ask for 12MbdData Sheet:The FT233HP/FT232HP supports a data transfer rate up to 12 Mbaud when configured as an RS232/RS422/RS485 UART interface.Please note the FT233HP/FT232HP does not support the baud rates of 7 Mbaud 9 Mbaud, 10 Mbaud and 11 Mbaud.

author: tooki
author_rank: Super Contributor
timestamp: July 14, 2023, 08:42:46 pm
content: Quote from: PCB.Wiz on July 14, 2023, 08:25:33 pmFYI, the board in question (USB-COM485-PLUS2, as is imprecisely stated in the thread title) uses the FT2232HQ, not the FT232HP/233HP, though the chip’s supported transfer rates are exactly the same.Oddly, the board‘s specs list a transfer rate of 10Mbps…My guess is that the 10Mbps is the maximum supported by the RS-485 transceiver chips.Anyhow, OP, see:https://ftdichip.com/wp-content/uploads/2020/08/AN_120_Aliasing_VCP_Baud_Rates.pdf

author: ajb
author_rank: Super Contributor
timestamp: July 14, 2023, 10:02:33 pm
content: Quote from: tooki on July 14, 2023, 08:42:46 pmfrom that pdf....QuoteEditing hex values in an INF file seems like a great way to fuck with someone you don't like, and a HORRID way to do literally anything else with this capability. I guess if you really need to get a nonstandard baud rate from an application that normally can't do that....Given that the windows COM port API and the FTDI direct driver can both just be given an arbitrary baud rate, though, does the driver only use the divider settings from the INF file when the requested baud rate matches one of the standard ones? So if you request a baud rate of 9599 or 9601, the driver/internal logic calculates the dividers and you get exactly those rates (or as close as the divider can get anyway), but if you request 9600 you get whatever divider settings the INF file has for that entry?

author: coromonadalix
author_rank: Super Contributor
timestamp: July 14, 2023, 11:58:09 pm
content: some companies added supplemental settings in / on some ftdi drivers, you could select more .... had such an adapter in the pastcant recall the model

author: PCB.Wiz
author_rank: Super Contributor
timestamp: July 15, 2023, 04:43:22 am
content: Quote from: tooki on July 14, 2023, 08:42:46 pmHmm, Looks like FTDI just lazily badged a Chinese product, complete with numbers that directly conflict with their own data sheetWhy not simply use a RS485 part thatcanmanage 12MBd ?Has anyone managed to actuallyget10MBd from a FT2232H ? All my UART divisor tests on the FTDI parts gave 24M/N as does the device data sheet!

author: tooki
author_rank: Super Contributor
timestamp: July 16, 2023, 02:56:43 pm
content: Quote from: PCB.Wiz on July 15, 2023, 04:43:22 amYeah, um, no.If anyone cloned anything, it was the Chinese cloning FTDI.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: July 16, 2023, 07:50:29 pm
content: Quote from: tooki on July 16, 2023, 02:56:43 pmI was talking about the pcb module/ docs, not the silicon.Thechipdocs agree with my tests, this module docs do not.We are still waiting foranyoneto report an actual 10MBd

author: tooki
author_rank: Super Contributor
timestamp: July 19, 2023, 11:12:20 am
content: Quote from: PCB.Wiz on July 16, 2023, 07:50:29 pmSo was I.It’sabsurdto think a chip manufacturer would copy some random Chinese design. A chip manufacturer has to design evaluation boards and stuff themselves anyway, as part of the design verification process. They don’t need to copy anyone else.On the other hand, the Chinese vendors copy others board designs all the time.Quote from: PCB.Wiz on July 16, 2023, 07:50:29 pmYeah, everyone understood that.Quote from: PCB.Wiz on July 16, 2023, 07:50:29 pmYup. We get that.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: July 19, 2023, 11:48:56 am
content: The FTDI D2xx driver reports an error when trying to set 10Mbaud. 6,8 and 12 are the only high rates possible due to divider limitations.From teh FT4232H datasheet :QuoteI'm sure the 10M in the data comes from the transceiver used, so a bit of a typo really, though in practice it will probably work to some extent at 12M

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: July 19, 2023, 11:59:18 am
content: Quote from: ajb on July 14, 2023, 10:02:33 pmI think this is a legacy thing from when Windows and/or comon application software didn't support odd baudrates. Don't recall details but there definitely was a time when this was necessary, not sure if the limitation was Windows itself or software like Hyperterminal. I'd imagine old software with nailed-in baudrates is not uncommon in the industrial worldI once used the INF file to set custom receive latency to improve performance, but now that Windows enforces driver signing, dicking around with the drivers, custom PIDs etc. is much more difficult for anything going to an end-user.