@ Skip,
I'm making up a Digikey order list.
I've got other non X9000 related stuff to get, so I figured to make one "complete as possible" order and save on shipping.
I am presuming your KiCad files are general/draft at this point, and actual board design and layout is still undefined.
The reason? I mention this is that the SN74LV244APW is a TSSOP package with a finer pitch over the pinout equivalant, wider pitched SN74LV244ADW in the SOIC package.
At this pincount, density of the SOIC is 2x a PDIP, where the TSSOP is 4x the density of a PDIP package.
There does not appear to be a PDIP equivalant for the SOIC packaged SN74LV02. LS yes, LV no.
The SN65176BP appears to be a thru hole PDIP. I socket all PDIPs if possible.
The BSS138 are SMT but the solder points are far enough apart and shouldnt be an issue either. The BS170 appears to be the thru hole equivelant but NA at Dighkey. Jameco has plenty but if that's all that was ordered, min shipping would not be worth it
You didnt call out the Schottky feeding the VSYS but a thru hole device that may be usable is the 1N5820.
The pullups and bypasses I'd like to see in thru hole as well.
Also, did you intend to use a bypass cap on the SN65176BP?
J3 appears to be a 2x6 IDC (male?) headr connector like/similar to the one used on the Xcat.
Rather than task the original EEPROM socket's Vcc point with supplying the new assy, I would recommend a different feedpoint via a (1x2 or more) IDC connector dedicated and bypassed for power.
Space permitting, the "or more" to be unused pins for potential future "flying connection" board interconnect(s).
The 5v feed would be from a (TBD) source on the personality board via "flying lead(s)".
Given the ability, I would also make the Pico "pluggable" on pins.
If there is (ever) a problem, it would make for easier diagnostics, repair and/or replacement.
The Pico's 133mhz clock may require sheilding/RF bypassing and being "on pins" may help to easily add this to the design if needed.
So far Digikey has everything I as looking to order, but my list is not complete
