UART->RS232 adapter that supports 1.5M?
#1
I'm planning to wire the RP64's UART to a DE-9 RS-232 port on an adjacent machine once I have it mounted, for easier access to the console. I'm looking around for appropriate level-shifting adapters, trying to find one that supports the RP64's default baud rate of 1.5M. Does anyone have such a device to recommend?

An alternate option is to slow down the baud rate in U-Boot and Linux, of course, but I'd rather have something that will work regardless of software settings that could change. However, that is an acceptable solution if getting a slower adapter is the easier option.

Thanks in advance!
#2
If the "DE-9 RS-232" you presented means a true "RS-232C port", the signal voltage is +-12V.
If connected carelessly, it may be electrically damaged.

Unless you have a specific reason, I think using a generic "USB-UART" device is the smartest way to go.
If so, it is easy to obtain, and you can buy it for about $2 at Amazon etc. in most countries.

The important point is to make sure that it supports 1.5MBPS.
#3
(08-08-2020, 06:47 PM)t4_4t Wrote: If the "DE-9 RS-232" you presented means a true "RS-232C port", the signal voltage is +-12V.
If connected carelessly, it may be electrically damaged.

Yes, you are correct—I was confused by several product listings advertising "3.3V to 5V" when that refers to the range of the converter chip's power supply, not to the actual voltage shifting occurring.

Quote:Unless you have a specific reason, I think using a generic "USB-UART" device is the smartest way to go.
If so, it is easy to obtain, and you can buy it for about $2 at Amazon etc. in most countries.

The important point is to make sure that it supports 1.5MBPS.

There are no spare USB ports on the other machine to connect a USB adapter.

It seems like most UART->RS232 chips are some variant of the MAX232 series, so there's not much decision-making to do. Supposedly some of these chips support 1.5Mbps throughput, but it may not be documented at all. I'll probably just end up using 115200bps in U-boot and Linux.
#4
(08-08-2020, 04:44 PM)Skirmisher Wrote: I'm looking around for appropriate level-shifting adapters, trying to find one that supports the RP64's default baud rate of 1.5M. Does anyone have such a device to recommend?

I suggest looking up the data sheet for the chip on any adapter you consider buying. The data sheet will say what speeds are supported. (You can usually find it quickly by searching the pdf for "bps" or "baud".) If the product listing doesn't state what chip is used, avoid it.

Do not trust the speed claims in cheap adapter product listings. I bought one that claimed to support 1.5mbps, but that claim was a lie. It has a CP2102 chip, and produces garbage at the RockPro64's default speed. Many other adapters use the same chip. I later looked up the chip's data sheet, which confirms that speed is not supported.

You can configure u-boot to pass a slower bit rate to the kernel and successfully launch linux that way, but some of the early boot process messages will still be sent at the default speed, so troubleshooting anything that early will be troublesome with an adapter that can't handle it.


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