On 7/7/2019 4:29 AM, Michael Brown wrote:
>     Looking at a 7i76e manual it's differential RS422 while the
>     example configs suggest at the FPGA level it's a 2 pin RX/TX deal,
>     is that right? One example shows a TX enable pin, but I don't
>     think this is implemented on a board like the 7i76e which is all
>     I'm trying to duplicate. Any insight on this?
> 
> I have no experience with rs422 or rs485, but i guess yes....

RS-422 is always differential.  It may be full duplex (which only
requires TX and RX) or half duplex (which adds a TX-Enable signal).

The 7i76 daughtercard requires two SSERIAL channels, one for the 7i76
itself (for the Field I/O signals), and one which gets exported via
the TB3 connector.

Both buses are full duplex and do not require a TX-Enable signal.

The SSERIAL communication between the FPGA and the 7i76 is via
standard digital logic levels.  The 7i76 provides an RS-422
transceiver for the SSERIAL bus on TB3.

-- 
Charles Steinkuehler
[email protected]

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