[NTLK] NewtonTalk Digest, Vol 118, Issue 5

Matthias Melcher m.melcher at robowerk.de
Tue Oct 10 15:45:04 PDT 2023

> On Oct 11, 2023, at 00:29, Noah Leon <moosefuel at gmail.com> wrote:
> Hi Matthias!
>> On Oct 10, 2023, at 15:00, newtontalk-request at newtontalk.net wrote:
>> Ah, good to hear that you got the plug working. Did you manage to get the sertial communication up too?
> So I bit the bullet and tried wiring up the power pins, and it works! I was able to charge the Newton with 7v over USB to a voltage regulator connected to the 4-cell power pins via your connector.

Yay! That is indeed great!

> So that’s great. Thanks Morgan for pointing me towards that document, I had googled it and not found it.

Ah, it's hidden because it was under an NDA back then, plus it was not even a finished document, so whoever leaked it could have gotten into a lot of trouble.

> However I’m not able to get the serial board working, it shows up in the Apple System Report, but I must have it wired wrong, since I don’t get any communication.

> I’m sort of working with three different documents to figure out the pinout:
> http://www.unna.org/incoming/interconnect.html
> http://www.unna.org/unna/apple/documentation/n2platform/n2-padg.pdf

Apple uses the RS-422 levels, but your converter delivers TTL signals. Technically, RS-422 is a differential signal, making it more stable against outside signals. TTL is 3V or 5V on a single pin per signal. Apple uses their own chip LTC1323 to generate the differential signal. You can use a second LTC1323 to get back to TTL, but those chips are no longer available. There are tons of other line driver chips other than there for a Euro fifty or so, but all that requires soldering.

There are ready made cables out there (https://de.rs-online.com/web/p/schnittstellenadapter-und-konverter/6877831), but they are very expensive because RS422 is mostly used in industrial measurement equipment. And that still does not guarantee that it works with the Newton.

There is a special case when using the dongle with RS232. The LTC1323 was designed specifically so that it can handle those signal levels as well.

So the best bet is probably to have a tiny PCB that has a level inverted on it. For more that one cable, it would make sense to make a PCB anyway, because hand soldering those connectors sucks.

> http://myapplenewton.blogspot.com/2019/04/the-incredible-shrinking-newton.html

This connector uses port 3 for that exact reason. Port 3 is CMOS level, but can handle TTL signals.

> This is the serial board I’m using: 
> https://www.amazon.ca/dp/B0CCF3C1YF?psc=1&ref=ppx_yo2ov_dt_b_product_details
> I’m just trying to figure out how to match this board to the existing pins.

I hope I explained that well. If I find the time, I will dig up my first attempt at this cable and get the driver chip.

 - Matthias

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