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Forum Index : Microcontroller and PC projects : Microbridge Fault

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SteveIzett
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Joined: 04/05/2023
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Posted: 11:32pm 15 Sep 2023
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Hi friends

Can anyone recognise these symptoms and offer the solution.
I built an Explorer 28.

On power up the Microbridge Mode LED flashes approx every 33 seconds.
If I push the Prog button it will respond with a flash after a few seconds, and then repeat flashing every 33 seconds.
Ive tried holding the button for more than 2 seconds (including over 10). No change.
The Prog LED never turns ON as it should.

On power up the Microbridge Pin 7 and Micromite Pin 1 MCLR goes HIGH for approx 2 sec then LOW, then within a few hundred milliseconds a short pulse HIGH, before holding in reset.

If I bridge the connector pins Console IN & OUT. Key presses on the serial emulator echo back and the Mode LED flashes to indicate reception pf chars.

When I snoop the Console OUT pin on startup the mmbasic startup message and prompt are transmitted during the 2 seconds that the MCLR pin goes high then its held in reset.

Momentarily pressing the Prog button yields the same as above and my Serial emulator reports its disconnected from the E28.
Holding the button releases the Reset pin as long as you hold the button.
Serial Emulator reports its disconnected from the E28.

So my fault finding has be thinking - The Microbridge is working as a USB to Serial AND the Micromite is alive.
What's wrong appears to be:
a. Microbridhe doesn't respond correctly to Prog Button being pressed.
b. Reset/MCLR pin being held LOW.

Ive checked connections carefully and retouched with flux multiple times under magnification and tested all pins (resistance) against the schematic.

Any help appreciated.

Steve
 
Turbo46

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Joined: 24/12/2017
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Posted: 12:31am 16 Sep 2023
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See this not sure if it is the same problem but it might help.

  WhiteWizzard said  With the MicroBridge unit, I strongly advise adding a 10K resistor between Pins 1 & 5.

This would have made your LED stay 'on' with no target device connected. What is happening is Pin 5 is the Rx pin (on the Serial Port), and it needs to be 'pulled high' to avoid noise making the Mode button 'less responsive'.

One important thing is that the MicroBridge DOES need to be connected to your console program for the RESET feature to work - this has caught me out on many a demo!!

WW


Bill
Keep safe. Live long and prosper.
 
SteveIzett
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Posted: 09:52am 16 Sep 2023
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Thanks Bill

I added the 10K to pull up the rx pin 5. It had no effect, but thanks.

Cheers

Steve
 
robert.rozee
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Posted: 11:48am 16 Sep 2023
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note - the pullup should be added to pin 5 of the 1455 chip (not pin 5 of the MX170). for most cases a pullup on pin 11 of the MX170 will act in much the same way.

did you program the 1455 yourself, or obtain it pre-programmed?

after connecting your E-28 to the USB port and running the terminal emulator you should see ONE LED illuminated. briefly press the 'select' button to enter programming mode. now press the '!' key and you should see the response "V1.18" on the terminal screen. next press the '?' key and you should see the response "ascii ICSP v1N" appear. now press the '4' key and you should be returned to the mmbasic interpreter.


cheers,
rob   :-)
 
robert.rozee
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Posted: 12:16pm 16 Sep 2023
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see schematic here:
https://www.thebackshed.com/forum/uploads/Grogster/2021-06-01_152422_E-28%20(1D)%20diagram.pdf

amendment to my above posting - it is (marginally) preferable for the 10k pullup to be on pin 11 of the MX170 rather than on pin 5 of the 1455. but if you have just the 1455 on a PCB alone, then the resistor can go straight to pin 5 of the 1455.

does your E-28 module have "Version 1D" silk-screened next to the regulator? or "1C" or "1B"?


cheers,
rob   :-)
Edited 2023-09-16 22:17 by robert.rozee
 
SteveIzett
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Posted: 02:22pm 17 Sep 2023
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Hi Rob

Thanks for the consideration.

I tried the 10K pull-up on the Connector Pin 11 which is Pin 5 of the Microbridge according to the SC article by Geoff.
I purchased the kit from Siliconchip with both PIC's pre programmed.
The board is marked 1D. I see on the schematic that I found that the 'D' version has the pull-up on the Micromite Pin11, as does the SC article schematic. I should have checked the circuit before trying the extra pull-up!

When I connect the E28 to my MacBook Pro running 'Serial' the power LED is ON and it recognises the USB device. The mode LED flashes with any key press and also flashes every 30 odd seconds.

I just now tried what you described:
Momentarily pressing the Mode Button causes the Serial application to report that the E28 disconnected before reconnecting about 2 seconds latter. The Mode light does not turn ON but simply flashes about 2 seconds after the ModeButton press and on each key press, and every approx 30 seconds thereafter.

As I mentioned in my previous post the MCLR pin goes high for about 2 seconds after startup and same after I push the Mode Button, before the MM is held in reset.

Does this make any sense?

Thanks

Steve
 
Turbo46

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Posted: 10:00pm 17 Sep 2023
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I have a Windows laptop and don't have an E-28 but I do have a backpack board with the Microbridge circuit included. It works as Rob suggested - and he should know.

If your LED is flashing every 30 seconds or so then I suspect that your Mac is sending something to cause that because it flashes for every character sent.

  Quote  MCLR pin goes high for about 2 seconds after startup and same after I push the Mode Button, before the MM is held in reset.

I guess you mean that MCLR is being held low. The MCLR (reset) is active low) and should be high for normal operation - I think it goes low for programming mode.

I'm not clear whether the Micromite is working or not, do you get the startup message on power up on your terminal emulator?

> Micromite MKII MMBasic Ver 5.05.03
Copyright 2011-2020 Geoff Graham
0

Bill
Keep safe. Live long and prosper.
 
Grogster

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Posted: 11:34pm 17 Sep 2023
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In Linux, I seem to recall that it tries to keep external serial ports alive by sending AT commands in the background.  Not sure if MAC does that also, but I mention it just in case.

When you give the SELECT button a firm press, the MODE LED should light AND STAY LIT - this indicates you are in programming mode.  At all other times, the MODE LED just blinks whenever there is any data going across the USB cable.

When I build the E28's, they are assembled with bulk-programmed 1455 USB chips, and blank 170 chips.  This is done on purpose, so that I can program each E28's 170 chip, using the pre-programmed 1455 USB chip.

That method allows me to ensure that the 1455 chip is working, the LED's are working, and the SELECT button is working, in order for the HEX file to be loaded into the previously virgin 170 chip.

I then check that I can talk to the console on the module, and then it goes in a test jig to ensure all pins are connected and working.

Therefore, I would have to say it is more likely to PERHAPS be the Mac trying to send some kind of wake-up AT commands in the background, to keep the port alive - which it does not need to do with any MM using the 1455, and that might be upsetting or otherwise confusing the 1455 chip.

That's my guess, anyway, and you have already done good testing on your own and proved that both the 170 chip and the 1455 are essentially working OK, so....

I know you have a Mac, but could you perhaps take the module to a chum with a Windoze 10 or 11 machine, plug it in there, and see if everything works as expected?

Good luck, and please do keep us updated.
Smoke makes things work. When the smoke gets out, it stops!
 
SteveIzett
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Joined: 04/05/2023
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Posted: 05:47am 18 Sep 2023
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Hi Guys

I've built 3 backpacks equipped with Microbridge PIC's and have had no issues with my MAC (To try it on a Windose machine, please, that's sacrilege!! )  Please be gentle!

As I wrote previously I went around the Microbride with a seperate USB to serial adapter powering the board and directly into the Console via the Pins 11&12 on the connector.
The Microbridge does exactly the same things. 3 other Microbridge equipped Backpacks have been fine.

The bridge is:
1. Acting perfectly as far as USB to Serial
2. Always flashing the mode LED every 30 sec, AND 2 second after any press of the Mode Button
3. Holding the MM in reset after 2 sec from power up or pressing the mode button, just long enough for the MM to send the startup and prompt before being held in reset.

The bridge is not:
1. Going into program mode (Mode LED lighting solid) on momentary pressing the Prog button.

My thoughts are, what would cause the Microbridge to act as its doing above:
   1. Is there a fault on the board I can't find, What circuit condition would cause the bridge to respond as it is doing
   2. Is the Microbridge code corrupted, but if so how is the USB to Serial running (Watchdog?)
   3. Is there noise on a rail (bypass cap failure)

I will put a Scope on the supply pins and check for noise tonight
I'll also check what the programming inputs on the MM are doing in case they could be effecting the Bridge PIC.

I'm struggling here! What am I missing?
 
Turbo46

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Posted: 05:57am 18 Sep 2023
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Do you get the startup message on power up on your terminal emulator?

> Micromite MKII MMBasic Ver 5.05.03
Copyright 2011-2020 Geoff Graham0

Bill
Keep safe. Live long and prosper.
 
SteveIzett
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Posted: 07:55am 18 Sep 2023
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Hi Bill

No, as its takes longer that 2 seconds for the Mac Serial Emulator to recognise the USB device (Microbridge) and connect.
I didn't know the MM was alive till I connected the seperate USB to Serial directly and when I did I saw the startup message but then it went dead. I was scratching my head until I put the scope on the MCLR pin and saw the 2 seconds out of reset at startup.

Steve
 
Mixtel90

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Posted: 08:16am 18 Sep 2023
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I can't see any easy ways to debug this as the fault could be in several places, possibly in more than one simultaneously. Personally I'd first try it on a Windows machine using Tera Term as that's the baseline setup that will definitely prove the computer end. If that doesn't work I'd change the Microbridge chip. I seriously doubt if there are hardware errors anywhere else as I'm sure we'd have heard of PCB faults.

I definitely wouldn't trust the Mac to be able to provide the correct serial interface to the Microbridge unless you have a second Microbridge to test it with first, using the identical current versions of the OS and terminal emulator. Just because it worked in the past, possibly before any "updates", doesn't mean it will work now. We know the Microbridge code is solid and has been for years (providing the chip itself isn't at fault).
Mick

Zilog Inside! nascom.info for Nascom & Gemini
Preliminary MMBasic docs & my PCB designs
 
robert.rozee
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Posted: 10:02am 18 Sep 2023
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hi Steve,
   from everything you have written it feels a lot like the 1455 has the wrong firmware programmed into it, perhaps the firmware for some other silicon chip project?

the 1455 chip itself (sans firmware) has fixed pins that can be used for USB, and fixed pins that the onboard UART can be routed to. hence, as long as the firmware programmed into it is for something/anything that plumbs together UART and USB it is likely to perform bridging functions - but not necessarily at the correct baud rate for the MX170, and pin 7 will still be holding the MX170 in reset (you could lift this pin).

the 'select' input, (1455) pin 4, is also the -RESET (input) pin of the 1455. with the correct ('microbridge') firmware loaded, this -RESET function is disabled, allowing pin 4 to be used as the 'select' button input. the fact that pressing the button resets the USB connection tells me the -RESET function is not disabled.


you'll notice that there are five square pads in a row near the 1455, labelled: 3v3, 10, 9, 4, GND. these are for connecting a PicKit3 programmer to load the 1455 firmware. how do you feel about attaching 5 fine wires and loading this firmware yourself? it may also be possible to load the firmware using another micromite, although it has been quite a few years since i last did this!

better yet - contact silicon chip and have them send you a replacement 1455. are you confident unsoldering the 1455?


cheers,
rob   :-)
 
matherp
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Posted: 10:18am 18 Sep 2023
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The instructions for programming a 1455 with a Micromite are on Geoff's site

https://geoffg.net/microbridge.html

Had to follow them myself just a few days ago   and all worked perfectly as written
 
JohnS
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Posted: 11:02am 18 Sep 2023
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  Grogster said  In Linux, I seem to recall that it tries to keep external serial ports alive by sending AT commands in the background.

Linux may do - but only if you have something set up to do that. I don't know how common it is for something to be installed & running by default.

It may be modem manager?

Just disable whatever does that unless you actually want it. (Same as for any OS if it does stuff by default that you don't want.)

John
Edited 2023-09-18 21:04 by JohnS
 
SteveIzett
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Posted: 12:21pm 18 Sep 2023
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I just checked 3 x backpack #3's with Microbridges that I have in process. All 3 function flawlessly with my Mac.
Never had any issues using the Mac and 'Serial' (emulation software)

I was told by Silicon Chip that there is only one version of the Microbridge Code.
I had wondered if there was code burnt into this chip but was for another project. And put in the kit by mistake.

As far as removing the PIC itself, I would cut the pins and then remove each pin separately. Is there a better way?

Thanks Robert, I like the idea of soldering a harness onto those pads and using my picKit3 to check the code in the 1455 match the right code - V1.18
I might get a chance to do this tomorrow afternoon.

I'll be very interested to see what's in it.

Thanks people.

Cheers

Steve
 
Turbo46

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Posted: 12:11am 19 Sep 2023
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I'm still curious about the LED flashing every 30 seconds.

Is it caused by something sent by the MAC?
Does it happen for the LED on a backpack if you plug one in?
Does it happen if you power the E-28 from a wall wart (i.e. power only)?

Bill
Keep safe. Live long and prosper.
 
Grogster

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Posted: 03:03am 19 Sep 2023
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At this stage, I am also inclined to agree with Rob, in that the firmware in the 1455 chip could be for another Silicon Chip project, and perhaps they just got some chips mixed up or something.

In your last post, you state that 3x backpacks with microbridges work fine on your MAC, so this is suggesting either the wrong HEX file in the 1455 chip you have been supplied, or it could perhaps be a bad chip or a corrupted HEX flash, but that is less likely, as the chips themselves are pretty tough, and if the flash verify fails, the programming fails, and the programmer would inform whoever was doing the chips, that this one failed to program.

Keep us posted!
Smoke makes things work. When the smoke gets out, it stops!
 
Turbo46

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Posted: 06:31am 19 Sep 2023
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Some history of the Explore 28

Bill
Keep safe. Live long and prosper.
 
SteveIzett
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Posted: 10:25am 19 Sep 2023
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Hi people.

I soldered ICSP to the 1455 and connected my PicKit3.
The MPLAB IPE reports that Target Device ID is invalid but appears to read the devices config bits.
The chip tests non blank
But the Memory shows all 00h's
When I try and verify to the V1.18.hex file it says it failed but that appears to be because it reads all memory locations as 00h

The Code Protection bit is set. Arrr.

I'll contact Silicon Chip and see what they have to say.

Cheers

Steve
 
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