RS-485 speed test rig


I just got started on a project all of the sudden that pretty much begins and ends at the speed I can squeeze out of various pieces of wire via RS-485.  To find out, I rigged up 2 Atmega48’s each with SN75176 RS-485 transceivers.  I happened to have those lying around (ok, stuck to various boards) because they ‘re what I use for DMX-512…

I had to start out by coercing a software UART into working, since the hardware UART is needed for the actual test channel.  The current challenge is to get the driver and repeater code to behave in the right sequence so I can actually start doing bulk testing at higher bit rates.  The obnoxious part is having to move around the AVR-ISP header.  My logic helper will fix that problem eventually, as I can just run 2 of the 8 ports to the AVRs, another couple as software-UART readout so I can watch both debug ports at once, and voila.

RS485 test


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