USB to RS485 converter
Cheap and popular USB to RS-485 converter.
From what I remember I've bought both my converters from the same brick-and-mortar store. They worked pretty fine as RS485 MODBUS adapters, but in February 2025 I've found a problem with one (and just one) of them. It looks like it is not compatible with the latest (from September 2024) Windows 10 64-bit CH340/CH341 serial port driver.
The issue: SetCommState function was failing with errno set to 31 (ERROR_GEN_FAILURE / "A device attached to the system is not functioning").
Installing manually CH340 driver from 2019 and forcing this version through device manager (might need to repeated multiple times) fixes this issue.
No physical difference from the outside. First one is not working, second one works.
While both adapters look similar inside and both have chips with no markings (both are fakes?), the first one has no crystal.
Maybe is should not be surprising, according to datasheet there are multiple CH340 variants, some requiring external crystal and
some with built-in crystal (is is really physical crystal or just PLL synchronized with USB?).
If markings on (likely fake) MAX485 are trustworthy, second adapter might be 6 years older than the first one.
This would mean that chip version having problem with the latest driver is the newer one.
6V8 transient voltage suppressor diodes are missing from the second one.
See also: https://www.digitaltown.co.uk/66FakeCH340Chips.php.
CH340 driver from 2019 (working with both my converters): CH341SER_WIN_3.5.ZIP.
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