Could you please restate your problem? Reading the thread, it looks like you've got successful character transmission from Master to Slave, but then you're printing them(to Serial Monitor) and they're not correct, or not appearing? If so, I suggest in your slave code, you add an else to that last if, and print whatever it was you received, like this:
Serial.print(incomingByte,HEX);
I expect you'll find that you're receiving something, just not what you expected.
Sorry, if this isn't what you're presently struggling with, but that's what I get from my read through.
Greg, if it works for you, go with it. While you're at it, tell TI they're full of bs if you want to. I can only tell you what's worked, and not worked, for me across 20 odd years of occasionally dealing with RS485 installations.
I might suggest, however, that you carefully investigate whether your portable is truly ungrounded, or incidentally grounded through some other connection, be it an RS232-USB adapter for some other device, an HDMI cable plugged into a grounded monitor, audio cord, to something, or some other path. That would more than suffice in all but an industrial setting.
By the way, if you plug in your Arduino via a standard USB cable, the Arduino ground is connected to the computer ground, which then would take care of referencing your RS485. So there's that.
In my case, an adapter like yours, I just soldered a wire to the inside edge of the USB shell and connected it to my Arduino's power ground. When I was struggling with this, a few years back, I suspect the Arduino USB ground path was what was tripping me up, because the issue came and went seemingly at random, but was likely consistent with unplug Nano A to reprogram it, in the process de-referencing Nano-B, which promptly caused the PC application I was running to talk to both to throw a hissy fit. @retgui1221 apologies for continuing this, but while I'm waiting for your progress, I figured I'd continue this side-thread in the open. We may end up splitting the thread, for cleanliness.
Diagram, post #1, shows DE&RE\ tied high on one unit, low on the other. If he's receiving anything (yet to be determined, see my previous message), then it's code, not wiring. TBD.
if the the RX pin (0) is being driven by the max chip, how is the arduino being programmed thru the usb I/F? is the connection being removed while programming?
i used an Arduino mega and Serial1 port to develop code to interface with another rs-485 device. obviously easier to debug
but using LEDs, perhaps an LED should simply be turned for a short while (delay (500)) on when the slave sees something, anything being received from the serial interface, then work on trying to determine what is received. that might be seeing if what is received is different that what was previously received
Normally, one RX input cannot receive from two TX outputs, for obvious reasons. Checking the Uno schematic, there are resistors in place to allow both the USB/serial converter on the Uno, and the external RX input, to drive the RX input on the '328. I would expect these to allow concurrent connection without damage, but signal interference is another matter. The RE\ pin on that MAX485 should be pulled high for uploading, certainly. As for normal operation, I would expect the USB signal to interfere with the signal from the MAX485 when the USB connector is inserted.
So yes, this is likely the problem.
@retgui1221 you'd be best to try an instance of Software Serial for receiving that data, and obviously, that will need different pins for RX and TX(can't have one without the other). If you do that, you can then keep the USB connected to ARD 2, and use Serial Monitor to display your incoming data.
i only brought this up because it can interfere during programming and asked how is the Arduino programmed when the RD pin on the MAX chip is enabled
but there doesn't appear to be a problem when the USB cable is not used and the Arduino is powered some other way.
as mentioned, i used an Arduino as a model RR controller connected to a command station with an rs-485 I/F. i doubt i even tried testing it with the command station with the USB cable plugged in. the USB interface may be like rs-485 and the USB TX pin is only enabled during transmission.
That's what I believe, as well. The OP hasn't indicated power method, but if he's leaving the USB plugged in(necessary to use Serial Monitor), then he's got a conflict he can't avoid unless he switches to SoftwareSerial.
His implementation, using VCC and GND for enable and disable, is limited as well. Really should be using a pin to enable/disable for transmissions; however, for this unidirectional test, that part isn't an issue.
solved, I did what @DrDiettrich told me and works on the sim(proteus)(i used the Max 487 which is quite similar, it doesn't have the VCC and GND connections),also it was never going to work on the physical slave because the f****** pin was burned. Sorry guys, my fault.
