Re: [NTLK] Interconnect second serial port (was: FDTI usb)

From: Adriano (
Date: Mon Mar 21 2005 - 10:30:57 PST

Thanks to your help something is clearer to me now, but i still do not
know how to use this infos for communicating with the second serial
port on the interconnect port.
Please let me explain better the tests and results i found working
around this:
the TX and RX output signals on the second serial port are not
specified if plus or minus, and i do not have the instrument for
accurate measurements. Although the lack for the right instruments
(i.e. oscillometer), i tried to have the second serial port
communicating using a TTL (Max232) level shifter adapter.
So i connected the Messagepad second serial channels to a rs-232 level
shifter using the 5V+, TX, RX and GND signals from the interconnect.
Then on the level shifter output i have connected a mac serial 8din
female connector which shows the level shifter output signals on TX-
(pin 3) , RX- (pin 5), with RX+ (pin 8) grounded on pin 4.
I have leds connected on both sides of the level shifter, so the led on
the Newton side light-up when i start any connection from the
MessagePad (thanks to the 5V output), instead the led on the level
shifter output light-up only if connect a rs-232 to usb adapter, NOT if
the adapter is a keyspan which translates a mac serial 8din connector
to usb.
Although i could assume that the board i have is pretty functional (as
the leds light-up on both sides), instead i still haven't had the
chance to see the MP2100 communicating anyway.
I tried to connect:
  - Newton Keyboard (no success)
  - Newton Fax (no success)
  - Docking on a Mac (again no success)

I am getting mad, so any help will be a breathe....


P.S.: pardon me if am offending any good technician present in this list

Il giorno 21/mar/05, alle 11:00, Johannes Wolf ha scritto:

Indeed it looks like that,
but Tx+ and Tx- are SYMMETRIC differential output signals of the RS 422
Tx+ ranges from 0 to + 12V and Tx- from 0 to - 12V.
When you apply an unipolar logic high signal (i.e. from the Cirrus
you get +12V at the Tx+ and -12V at the Tx- output at the same time,
but the
converting the symmetric signals back to unipolar logic using a
input, you recover the original signal in the first place.
But dependent on the levels, a differential input connected to 0V and
might interprete the signal correctly and indeed then you have the
signal of the original input.

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