[fpc-pascal] Arduino project

[Christo Crause]

Adriaan,

Typical digital I/O pins can only read single ended values (the pin voltage
is interpreted relative to the common ground reference).
RS-422 is a differential signal measured between two wires, not relative to
common ground.  The Github example you mention below is specifically for a
single ended electrical interface, the encoder only has a single data
connection (D0).  Your original specification mentioned the SSI line driver
is RS-422, therefore you need an RS-422 to TTL converter.  The clock signal
may also be RS-422, check encoder datasheet. Arbitrary reference for a
longer explanation: https://electronics.stackexchange.com/a/160552

Christo

On Fri, Sep 11, 2026 at 9:55 PM Adriaan van Os <adriaan at adriaan.biz> wrote:

>
> Christo,
>
> Thanks for the reply.
>
> > You need an RS-422 to TTL converter to read the absolute rotary
> > encoder pulses, the diagnostics can be read by any digital input pin
> > (after level shifting of course).
>
> Why is the converter needed ? Because of voltage differences ? This
> example project <https://github.com/atarbabgei/absoluteEncoderSSI> seems
> to connect the encoder directly to the Arduino.
>
> But I see lots of RS-422 to TTL converters on amazon.fr
>
> Thanks,
>
> Adriaan van Os
>
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