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dcsbios - Can I use an Arduino Mega as an RS485 slave?


Bullant

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I'm finally getting around to converting to an RS485 setup, and my test with a mega as master and uno as slave went well.

 

However, my UFC has a LOT of input requirements and is currently running on a mega. Any attempt to run a mega as a slave is resulting in absolutely nothing happening. I have the TX/RX wires running to D0/D1 just like the UNO.

 

So can someone confirm if it is actually possible to use a mega as a slave?

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Hi AndrewW,

 

 

I did a working quick setup (only the master caution LED on D13) with the following Mega as slave and Uno as slave configs:

 

 

DI -> TX0 (D1)

RO -> RX0 (D0)

DE/RE -> D2

 

 

So it's confirmed in principle.

Regards, Vinc

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Thanks, appreciate the effort. Must be an issue on my end, will try again.

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Cheers mate, still waiting for a chance to have another go with mine, must have had something wired up wrong.

Intel i7 13700K @ 5.3 GHz / ASUS TUF Gaming Z490-Plus / 64 Gb G.Skill DDR4-3600 / RTX 4090 / 2TB Kingston KC3000 NVME / Win 10 x64 Pro / Pimax Crystal / WINWING F/A-18 HOTAS

A-10C, AJS-37, AV-8B, F-4E, F-5E, F-14, F-15E, F-16, F/A-18C, F-86F, FC3, Christen Eagle 2, FW190D-9, Mosquito, P-47D, P-51D, Spitfire, AH-64D, KA-50, UH-1H

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Cheers mate, still waiting for a chance to have another go with mine, must have had something wired up wrong.

 

Not necessarily. I got a batch where some of the Max487 chips were bad. I eventually figured out that it could easily be identified as they ran really hot. So maybe the wiring is ok but the chips are bad.

 

Cheers

Hans

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Not necessarily. I got a batch where some of the Max487 chips were bad. I eventually figured out that it could easily be identified as they ran really hot. So maybe the wiring is ok but the chips are bad.

 

Cheers

Hans

 

Thanks for the tip, but I swapped out the mega for a Uno with exactly the same 487s setup on the breadboard and it worked fine. So had to be something weird with the mega.

Intel i7 13700K @ 5.3 GHz / ASUS TUF Gaming Z490-Plus / 64 Gb G.Skill DDR4-3600 / RTX 4090 / 2TB Kingston KC3000 NVME / Win 10 x64 Pro / Pimax Crystal / WINWING F/A-18 HOTAS

A-10C, AJS-37, AV-8B, F-4E, F-5E, F-14, F-15E, F-16, F/A-18C, F-86F, FC3, Christen Eagle 2, FW190D-9, Mosquito, P-47D, P-51D, Spitfire, AH-64D, KA-50, UH-1H

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Weird, tried again with a brand new clean mega as the slave and a very simple sketch turning on the LED tied to pin 13 with the master caution.

 

Worked perfectly ... then stopped. The slave 487 chip was super hot ... swapped it out and now it's not working at all again. Could be a problem with my breadboard, will investigate further when I have more time.

Intel i7 13700K @ 5.3 GHz / ASUS TUF Gaming Z490-Plus / 64 Gb G.Skill DDR4-3600 / RTX 4090 / 2TB Kingston KC3000 NVME / Win 10 x64 Pro / Pimax Crystal / WINWING F/A-18 HOTAS

A-10C, AJS-37, AV-8B, F-4E, F-5E, F-14, F-15E, F-16, F/A-18C, F-86F, FC3, Christen Eagle 2, FW190D-9, Mosquito, P-47D, P-51D, Spitfire, AH-64D, KA-50, UH-1H

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Nevada, Normandy, Persian Gulf, The Channel, Syria, Mariana Islands, South Atlantic, Sinai

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I am pretty much at my wits end here.

 

I have a UFC that has a mega behind it.

I have a switchbox that has a uno behind it.

 

Both work perfectly connected direct to the PC via USB.

 

I have a second mega configured as a master and hooked up through two 487MAX chips on a breadboard.

 

If I modify the sketch for the switchbox and hook it up it works fine.

If I do exactly the same thing for the UFC nothing happens.

 

In both cases I am using the same wiring on the slave

 

DI -> TX0 (D1)

RO -> RX0 (D0)

DE/RE -> D2

 

I have a third mega that I hooked up and wrote a very simple sketch to hook up the internal led to the master caution. I swear this worked once, but not since.

 

I noticed on my maser that the RX led flashes rapidly and continuously, but not the TX led which does not appear to do anything. Is this normal?

 

Any other suggestions? Because at this stage I am looking at just running a second usb cable for the USB, or rewiring it to use multiple unos ...

Intel i7 13700K @ 5.3 GHz / ASUS TUF Gaming Z490-Plus / 64 Gb G.Skill DDR4-3600 / RTX 4090 / 2TB Kingston KC3000 NVME / Win 10 x64 Pro / Pimax Crystal / WINWING F/A-18 HOTAS

A-10C, AJS-37, AV-8B, F-4E, F-5E, F-14, F-15E, F-16, F/A-18C, F-86F, FC3, Christen Eagle 2, FW190D-9, Mosquito, P-47D, P-51D, Spitfire, AH-64D, KA-50, UH-1H

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If your confident your wiring is good then you probably had a bad batch of 487's. I ordered 25 RS-487 from China and they were mostly crap. They ran super hot and then stopped entirely. I reordered from another supplier and they were all good.

 

Don't let that get you discouraged. I run several Mega’s as slaves and lots of Pro Minis without issue. So I know it works.

 

Btw, the Rx flashing on the master is normal. Very little flashing on tx is also normal.

Regards

John W

aka WarHog.

 

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Thanks guys, it's weird uno as slave works, mega on the exact same 487 chips doesn't work.

 

Away for work at the moment but will re-attack on the weekend.

Intel i7 13700K @ 5.3 GHz / ASUS TUF Gaming Z490-Plus / 64 Gb G.Skill DDR4-3600 / RTX 4090 / 2TB Kingston KC3000 NVME / Win 10 x64 Pro / Pimax Crystal / WINWING F/A-18 HOTAS

A-10C, AJS-37, AV-8B, F-4E, F-5E, F-14, F-15E, F-16, F/A-18C, F-86F, FC3, Christen Eagle 2, FW190D-9, Mosquito, P-47D, P-51D, Spitfire, AH-64D, KA-50, UH-1H

Combined Arms, WWII Asset Pack, China Assets Pack, Super Carrier, Falklands Assets

Nevada, Normandy, Persian Gulf, The Channel, Syria, Mariana Islands, South Atlantic, Sinai

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