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HowTo: Build a 16 Ch PicDimmed Renard with SSRs onboard!
( Dave Johnson)
Step 22 : RS232 VS. RS485
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| | Above are two pictures of an identical 8 channel Renard output from Vixen. The left image is the RS232 protocol, the right is after it has been sent through a RS485 converter.
We will start with a short discussion on RS232. In RS232, there is ground, and TXD (Transmit data, the dark blue line in the picture). TXD goes from ground to VCC. Ground is ground, and is therefore intuitive and pretty simple. In the picture above you can see the divisions are 200mV so in this case TXD goes from 0 to 1.5 Volts.
In RS485, the A signal (dark blue) goes from 0VDC to +.5VDC, while the B signal (light blue) goes from 5VDC to 0VDC. The resting or “no data” state of RS485 is A = .5VDC and B = 0VDC. The active state or “data being sent” state of RS485 is when A= 0VDC and B = 5VDC. Thus you can see, the signals are differential, one goes high, and the other low, for the transfer of one bit of data.
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