On Tue, 20 Jun 2017, Andrew wrote:
Date: Tue, 20 Jun 2017 22:33:43 +0300
From: Andrew <pkm...@gmail.com>
Reply-To: "Enhanced Machine Controller (EMC)"
<emc-users@lists.sourceforge.net>
To: "Enhanced Machine Controller (EMC)" <emc-users@lists.sourceforge.net>
Subject: Re: [Emc-users] Mesa 7i47S issue
2017-06-17 20:15 GMT+03:00 Andrew:
2017-06-17 18:34 GMT+03:00 Danny Miller:
Similarly the inputs aren't true differential, they're an optoisolator's
input diode with a series resistor to produce the rated trigger current
when +5v is applied + to -. Due to some esoteric details in how the bus
switch drive output works, these work best if you tie the + to +5v and use
the pin to drive the - to gnd. The signal is weaker if you do it the other
way.
Thanks for the tip!
I was going to try the weaker way.
If there's a series resistor, it's safe to drive full 5V between /RX and
RX.
7i47s has GND and 5V pins near RX terminals, pretty handy to connect
either way.
Well today I spent a couple of hours trying to get that alarm signal to
7i47s
This was my basic idea
[image: ?????????????????? ???????????????????? 1]
This connection IIRC caused flickering LED (with termination jumper off).
I tried replacing RX and /RX wires, still nothing.
It doesn't look like there's an optocoupler input between RX and /RX...
Also I tried experimenting with RX0 input and I think something's got
broken, because now I can turn it on/off with termination jumper
left/right. Other inputs doesn't work like this.
This is not unexpected, the card is probably fine
The 7I47S has differential inputs, They are not designed to interface with
single ended signals but can if needed.
The only way the inputs will work reliably is to have a positive differential
voltage across the inputs in one case and a negative differential voltage in
the other case.
If you have single ended say 5V signals you wish to read what you can do is
this:
Make a low impedance voltage reference of 2.5V with 2 series 100 Ohm
resistors from the 7I47S 5V pins.
Connect this 2.5V reference to the inverted input pin of all the 7I47S inputs
you wish to use, then connect your 5V single ended signals to the non-inverted
inputs. Now when you input signal is 5V the input pair see +2.5V and when
input signal is 0V, The input pair see -2.5V
(this will only work with termination off)
Peter Wallace
Mesa Electronics
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