RS485 Tranceiver IC's RX Pin

[ericthegeek]

Originally Posted by StephenYim

You can see the Frequency is 20Hz, with 5V amplitude(RDM-100 is power by USB). And the Dir Pin of the RS485 Tranceiver IC(SP3075EEN:RE & DE shorted together) also has the same waveform as the RX pin, only with 3.3V amplitude(the CPU is STM32F103).

I see what you're talking about. When the RE#/DE pins (shorted together) are low, the 485 line driver's receiver is active. The line driver will read the idle state on the bus and thus drives the "RX" signal high. But, when RE#/DE is taken high, most 485 line drivers will tristate the RX pin, so it will be floating unless there is a pullup resistor. This doesn't mean it's working or not, you're just seeing normal 485 line driver behavior.

Originally Posted by StephenYim

I am thinking of giving up this RDM-Controller and buy another one. Do you have any good suggestion, better with a cheap price,thanks.

I'm probably biased because I build DMX/RDM test equipment. But in my experience good test equipment is not cheap.