[NTLK] TTL serial cable: are they useless?

[Rufus Kohn]

Thank you Bernie for taking the time to clarify the difference. You made it very clear.

Rufus Kohn



.
 
  

> Op 12 mei 2019 om 03:34 heeft web at kobier.id.au het volgende geschreven:
> 
> Hi Rufus,
> 
> The simple answer is the TTL cable is no good..
> 
> BUT the long answer is
> 
> The difference between the TTL cable and the RS232 cable is the voltage levels used.
> 
> TTL uses TTL voltage levels of 0V for 0 and 5V for 1
> RS232 uses between +3 and+12V for 0 and -3 and -12V for 1
> 
> TTL cables are intended for direct connection to say a microcontroler but RS232 is intended for long distance communications.
> 
> To add to the confusion the Newton actual uses RS422 for the data comms which is a differential singling system which is basically double RS232 it has 2 transmit lines and 2 rx lines (one is the inverse of the other) to use rs232 you tie one to ground and use the other (to maintain the correct voltage polarity for the signal)
> As you might have noticed RS232 (and422) have a wide valid voltage range 3 to 12V so it is possible to invert the TTL signal with a CMOS inverter and it usually works. The CMOS inverter is required because it can accept a possible 12V into it.
> 
> Sorry the more I type the more involved this is becoming :-)
> 
> Now depending on the ACTUAL voltage output by the Newton - it could be anywhere from 3 - 12V Ive never measured it but if it is no more than 5V it could be possible to use the +Ve data pins (6 and 7) and tie the -Ve data pins 3 and 5 to gnd (this is the opposite to what is required for RS232 ) and use the TTL cable. NOTE I have not tried this or made the appropriate measurements it is just theoretically possible. I would not just TRY it with out making measurements first or damage may result.
> 
> Regards
> 
> Bernie
> 
> 
>> On 12 May 2019, at 06:19, Rufus Kohn <rufuskohn at gmail.com> wrote:
>> 
>> Hi
>> I bought a TTL serial to usb cable and found out it wont work with the
>> Newton. The mac recognizes the FDTI chipset but it is not possible to
>> connect via NCX. So i bought the correct cable but it left me wondering
>> exactly whet the difference is between the two.
>> They look identical.
>> Is the difference hardware? Like are the wires hooked up in a different
>> way? Could I switch them around to make it work?
>> 
>> Or is it a software difference and it will never work on a newton?
>> Who can enlighten me?
>> -- 
>> Met hartelijke groet,
>> 
>> Rufus Kohn
>> 0613159031
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>> http://newtontalk.net/
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>> 
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