HW: Termination on i/p and o/p RS485 pairs
For version 4 of conv-ttl-rs485 board, all rs485 pairs have been treated
strictly as differential pairs, with 120Ohm differential impedance.
(This was not the case in previous
version).
The board also has existing (from previous versions), optional,
termination for input and output as described in section 2.2 of the
conv-ttl-rs485 User
guide.
This optional termination is 100Ohm, which does not match the differential pair impedance on the board (now 120Ohm).
A new execution of the board would be necessary, with replacement of resistors for adequate values. Currently 2 parallel 200Ohm resistors are used to make 100Ohm. In order to keep the same footprint, we'll require 2 240Ohm resisotrs instead.