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MustardMan

Senior Member

Joined: 30/08/2019
Location: Australia
Posts: 175

Posted: 09:55pm 19 Sep 2019

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I am implementing an RS485 interface using the Explore 100 and noticed a problem with the latest PCB revision (v1D) and the MikroBUS. I don't know if it applies to earlier PCB revisions.

According to the documentation on Geoffs site (for the older PCB) as well as the newer schematic (v8 for PCB 1D - thanks TrevorH)...
- The MikroBUS Tx pin is connected to CPU pin 25.
- CON8 pin 29 is also connected to the CPU pin 25.
- CPU pin 25 can be accessed using COM3 in MMBASIC.

However in reality this does not appear to be the case. When I put a signal on CPU pin 25 (using it as COM3) it appears on CON8 pin 29 as expected, but it does not appear on the MikroBUS Tx pin. In fact the signal does not appear on any of the MikroBUS pins.

I haven't started a search for the Explore 100 PCB v1D layout yet to find out what the MikroBUX Tx and Rx (and indeed other pins) are connected to (my next step), but I've also noticed other errors in the schematic... v8 schematic (for v1D PCB) indicates the "5V" pin of the MikroBUS is connected to the Micromite 3V3 rail, which it is not - it is actually 5V as it should be.

Tracing the PCB tracks is another option, but might be difficult if the tracks are on the inner layers. I must say I didn't expect this much difficulty getting my project going!

Any insight as to what the actual MikroBUS connections to the CPU are?

Thanks,

TassyJim

Guru

Joined: 07/08/2011
Location: Australia
Posts: 5898

Posted: 10:34pm 19 Sep 2019

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I don't have a board to test but this might be the reason:
https://www.thebackshed.com/forum/ViewTopic.php?TID=8796&P=5#99289
There is/was a set of jumpers that allow you to swap the TX and RX lines.

Jim

VK7JH
MMedit MMBasic Help

MustardMan

Senior Member

Joined: 30/08/2019
Location: Australia
Posts: 175

Posted: 12:02am 20 Sep 2019

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Thanks for the tip - that was exactly the problem. I can see that my schematic is going to end up with a considerable number of handwritten notes on it!

Cheers,

panky

Guru

Joined: 02/10/2012
Location: Australia
Posts: 1094

Posted: 12:06am 20 Sep 2019

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@MustardMan

I have a blank board here and have traced all the click pins. They are correct as labelled on the PCB - the only error I can find is the 1D schematic showing the +5V Microbus pin is going to 3V3 - this is wrong, it does physically go to 5V.

As Jim has pointed out, the TX Rx lines go via a small jumper pad just below CON8. If you solder bridge the pads as per the little white marks, Tx on the Click board will go to pin 25 on the cpu which is MM COM3 Tx. Similarly for Rx.
The intent was I believe to allow swapping the RX/Tx lines to the click board as required.

Note also that the I2C lines can be pulled to 3V3 or 5V by the 2 alternative resistor arrays at the top of each click board.

panky.

PS. I have an operational E100 here also and am happy to assist any time - PM me if necessary.

... almost all of the Maximites, the MicromMites, the MM Extremes, the ArmMites, the PicoMite and loving it!

Tinine
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Joined: 30/03/2016
Location: United Kingdom
Posts: 1646

Posted: 09:11pm 20 Sep 2019

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Yeah, this threw me off in the early days. Not documented.

I stumbled upon the solution from a random post on here.

I love the whole Click module concept.

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