wriver4 - Posted 27 Hours Ago
I realize NCT5104D is configurable.
The customer has seen the board and wants to use com1 to connect the 5v modbus "proprietary RS485" to it.
I am having significant difficulties explaining to them why using com1 is a really bad idea.
This is not a deliverable at this point in time but comming soon.
I have other deliverables before this one.
Can someone give me a how to about the easiest way of creating a full ( = com1 5v capable) comX port?
Hi wriver4,
Using COM1 is strongly not advised, since firmware is printing messages to that port. It could be also used in the OS as a console.
From looking at apu3c schematics COM2 has no flow control pins exposed on J4 header.
By looking at page 12 on apu3c4 schematics: https://www.pcengines.ch/schema/apu3c.pdf
the only solution I can see is to use 4th uart on nct5104d, since 3rd uart is connected to PCIe expansion (see page 17).
All necessary uart signals would be provided on J20 GPIO header pins 11-18, inputs are 5V-level TTL and outputs have 12mA source-sink capabiity.
Additionally You have GND and 5V on pins 19-20. You can possibly enable this uart in firmware by enabling UARTD in sortbootorder (Payload [setup] option in SeaBIOS).
I am not 100% sure however if flow control will work, IMO it should. Also I would have to check whether the outputs drive 5V level or 3.3V level as nct5104 power supply.
Given that You would have full UART which You could then connect to a UART-RS485 converter or something like that.
This is the easiest way I can now think of.
Good luck.
