[NTLK] USB to Newton Interconnect cables

davida at pobox.com davida at pobox.com
Fri Feb 5 18:39:52 EST 2016


That’s actually one area I suspect I should prototype thoroughly.

There are two serial ports on the Interconnect port: one using a Linear Technologies LT1323 line driver, one with raw CMOS levels.  The default port is SCC channel 0, which has the line drivers, and I’m kinda tempted to use that because it avoids the need for a package on the Newt to enable the second port (SCC Channel 3).

The Interconnect doc from Apple states that the drivers on channel 0 use RS422 signalling.  I’ve grabbed a copy of the LT1323 datasheet, but haven’t had a chance to read it in detail yet, but … it might then be best to use an RS-422 driver from the USB bridge, rather than an RS-232 driver.  The MAX driver is the default part here, but I haven’t looked at its datasheet yet either.

So .. you’re absolutely correct to highlight this as an issue with the design.  Once I’ve perused the datasheets, I’ll come up with a proposal, and run it past the group for comment before doing a prototype to test it out for real.




d


> On 6 Feb 2016, at 09:41, newton at chichak.ca wrote:
> 
> Hi David.
> 
> Yes, my walnut brain finally clicked back into its socket.
> 
> What you are proposing is almost right then.
> 
> The output of the FTDI chip is intended to be connected to a processor directly. It’s low voltage stuff.
> 
> You will need to put another chip on the output of the FTDI chip to convert it into RS232 signal levels. Look at something like a MAX3232 chip from Maxim.
> 
> 
> Andrei
> 
> 
>> On 2016-February-05, at 2:38 PM, davida at pobox.com wrote:
>> 
>> Hi Andrei,
>> 
>> (skipping the internal port vs interconnect port confusion)
>> 
>>> I have some concerns, you say you are looking at using USB A connectors. Those are the ones that you have on your PC. These are for Host side devices, you will be making a device and should be using a B.
>> 
>> My plan, thus far at least, is to make a cable that will have a USB 2.0 (?) type A male connector on one end (suitable for plugging into a PC, Mac, Raspberry Pi, standard USB hub, etc), and FTDI USB-serial bridge in the middle, and the Newton Interconnect port on the other end.
>> 
>> My understanding is that if it was to be a “dongle”, that the upstream port on the dongle should be a type B, but that since the cable is embedded in the device (well, the device is embedded in the cable, really) that a type A is the right choice.
>> 
>> I’ll be posting full specs, prototype pictures, etc, for everyone to review before I proceed to actually making the main batch, and I’d really welcome reviews and suggestions (then, or any time).
>> 
>> 
>> 
>> 
>> d
>> 
>> 
> 
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