Just an FYI... I've been using the FTDI DB9-D5-M interface for several years now. This one install in place of a DB-9 connector and provides 5V TTL compatible signals for a full UART interface. I also used this interface on my recent C02 Pocket SBC which interfaces to a NXP SCC2691 UART. The hardware design uses RTS/CTS handshaking which is also supported in the BIOS for the SBC. Note that this device gets power from the USB connection but does not provide power outside (to the 9-pins).

I've been running a test program looping in EhBasic for the past 5 days or so attached to a USB port on a MacBook Pro using Serial as the console terminal program (native OSX app). I wound up downloading a system update which required a couple reboots of the system, so everything was shut down. When it finally rebooted and I logged back in, I launched Serial and the Pocket SBC picked up on the Basic program looping where it left off... nice. Of course, this does imply that you don't lose power to the USB port or the FTDI device goes offline and the UART and BIOS gets tanked.

I've also put the MacBook in suspend mode multiple times over the past few months with the Pocket SBC running some level of looped code tests and it's always recovered from where it left off. It's a nice easy test to see if the BIOS code is working with the RTS/CTS hardware configuration.

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Regards, KM
https://github.com/floobydust