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  1. #1
    Junior Member RobSchade's Avatar
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    Default Newbie to the forum

    Hi everyone

    I'm a newbie to the forum but not to Proton Basic. I've been using ProtonIDE for about 10 years on and off. Most of the projects were very basic with not much use of the highly integrated peripherals found in the latest PICs.

    So now I've been tasked with programming a High Temperature PIC, the 18F25K80 because it's got built in CAN and can work at elevated temperatures. Talk about being dropped in at the deep end!

    Hopefully there's enough info on the forum and the Microchip website.

    All the best

    Rob

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    Prolific Poster rcurl's Avatar
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    Default Re: Newbie to the forum

    Hi Rob-
    Welcome! Glad you joined us. I've never used a high temperature PIC. Very curious what you're up to (if it's not a secret!).
    We've got a few users on the forum that have done a lot of work with CAN connectivity. Let us know how it goes and we'll pitch in and help as best we can.

    -Rick

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    Senior Member tumbleweed's Avatar
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    Default Re: Newbie to the forum

    Rob -

    When you say the 18F25K80 can work at elevated temperatures what are you referring to?
    AFAIK, it has the same temperature specs as pretty much all the other chips (125 degC max)

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    Junior Member RobSchade's Avatar
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    Default Re: Newbie to the forum

    Hi tumbleweed

    my mistake, I should have been more specific. There is a variant of the standard part, PIC18F25K80-H/SS (available from Mouser, their ref. 579-PIC18F25K80-H/SS) which is specified to run at 150 degC.

    Rob

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    Junior Member RobSchade's Avatar
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    Default Re: Newbie to the forum

    Hi Rick

    Thanks for the offer to help, I'm bound to need it! The project is for a high voltage power supply that converts 100VDC - 600VDC to three voltage rails, 48VDC, 24VDC and 5VDC with a maximum (theoretical) combined power rating of 200W. The PCB is 30mm x 190mm and has to fit in a stainless housing, a long tube, that can withstand 15,000psi and temperatures in excess of 125 degC. The PIC isn't doing much and the only reason for using the PIC18F25K80-H/SS is it's one of the lowest spec' PICs that has the extended temperature rating (150 degC).

    All it's doing is getting two temperatures via I2C and sampling six analog variables, the current and voltage of the three supply rails. The potentially awckward part is it has to "listen" on a 512Kb CAN bus for a request for the telemetry data.

    I've only just started (yesterday) so very early in the firmware development of the project . It took me about 3 months to design and test the circuit/PCB and now comes the "interesting" part.

    I've basically got one loop getting all the telemetry and was going to have an interrupt handler to deal with the requests. The requests are infrequent, probably every few seconds so an interrupt will not impact on the gathering of data.

    So far I've got the main loop working and now have to sort the CAN side of things. On interrupt it will check if the request is for the HV PSU and if so it transmits 2 packets of CAN data (total 8 words) before returning to the main loop to continue to update the arrays setup for the data.

    So, onward and ever upward!

    Rob
    Last edited by RobSchade; 12th December 2019 at 14:33.

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    Junior Member RobSchade's Avatar
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    Default Re: Newbie to the forum

    Just out of interest, has anybody actually used the 18F25K80 CAN module?

    It's slow work ensuring all the configuration is correct, especially with the "helpful" data sheet provided by Microchip. I'm struggling to get the data I need about the bit assignments in the config registers.

    Rob

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    Prolific Poster rcurl's Avatar
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    Default Re: Newbie to the forum

    Quote Originally Posted by RobSchade View Post
    Just out of interest, has anybody actually used the 18F25K80 CAN module?
    Rob
    You project sounds interesting (and challenging).
    Our resident CAN bus guru is Bob, RGV250. He's done a lot of work with it and has created a CAN library. Hopefully he will chime in on this.

    -Rick

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    Prolific Poster RGV250's Avatar
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    Default Re: Newbie to the forum

    Hi Rob,
    First off, the library I wrote will not work with the 18F25K80 or any of that series, I am looking at it but they have changed things for no apparent reason.
    You say it listens for the request, another reason why the library will not work, when I was studying everything for this the general consensus was that the request (RTR bit) was virtually never used and most devices sent the data periodically and the receiving node could decide to use it or not.
    512kbit is quite fast, you say you have designed the board, I also read that at faster speeds board design can be critical, I assume it is due to capacitance around the transceiver but may be wrong.
    Do you know what the node/message ID needs to be as you will need that for some of the parameters, do you know the node/message ID of the device requesting the data?

    I forgot to add, is it straight CAN, CAN open, CAN FD etc

    Regards,
    Bob
    Last edited by RGV250; 12th December 2019 at 21:03.

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    Junior Member RobSchade's Avatar
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    Default Re: Newbie to the forum

    Thanks Nick, much appreciated.

    Rob

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    Junior Member RobSchade's Avatar
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    Default Re: Newbie to the forum

    Quote Originally Posted by RGV250 View Post
    Hi Rob,
    First off, the library I wrote will not work with the 18F25K80 or any of that series, I am looking at it but they have changed things for no apparent reason.
    You say it listens for the request, another reason why the library will not work, when I was studying everything for this the general consensus was that the request (RTR bit) was virtually never used and most devices sent the data periodically and the receiving node could decide to use it or not.
    512kbit is quite fast, you say you have designed the board, I also read that at faster speeds board design can be critical, I assume it is due to capacitance around the transceiver but may be wrong.
    Do you know what the node/message ID needs to be as you will need that for some of the parameters, do you know the node/message ID of the device requesting the data?

    Regards,
    Bob
    Hi Bob

    Thanks for replying so quickly, much appreciated.

    I have control of both ends of the comms as I designed the other end as well. The master node communicates with another board I designed (controlling a 3-Phase brushless DC motor) and will now be collecting data from the HV PSU board. The other two boards are not using PICs otherwise I would just use the code I used in them. I used a Parallax Propeller running at 80MHz with a code object developed by another programmer. It is capable of 1Mb/s CAN but at the moment I'm running it at 512Mb/s.

    Because the system is being upgraded, one module at a time, for a higher temperature rating, I can't use the Propeller and have to go to the High Temperature PIC.

    The problem I'm having at the moment is trying to setup all the registers to allow the CAN module to generate an interrupt so I can just transmit the 2 packets of data. I also have to ensure the baud rate is configured for 512Kb/s.

    I'm trying to see how another PIC was configured and then "port" the code over. Unfortunately, Microchip keep changing the names of registers and not providing any details of what the bits are in the registers. This is new to me because I've found previously that Microchip are pretty good with their data sheets.

    Oh well, onward and ever upward.........hopefully

    Rob

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    Prolific Poster RGV250's Avatar
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    Default Re: Newbie to the forum

    Hi,
    It is not the CAN settings that generate the interrupt but the interrupt registers, have a look at PIR5, PIE5 & IPR5.
    Can you edit the other boards, if so I would just send the data periodically, that way you do not need to worry too much about the interrupt.

    Bob

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    Junior Member RobSchade's Avatar
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    Default Re: Newbie to the forum

    Thanks Bob

    I'll look at that tomorrow.

    I really appreciate your help along with the others who have posted.

    Rob

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    Senior Member tumbleweed's Avatar
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    Default Re: Newbie to the forum

    There is a variant of the standard part, PIC18F25K80-H/SS which is specified to run at 150 degC
    Thanks, Rob. I see that now.

    I wasn't aware of that part, so it's good to know there's an option.

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    Junior Member RobSchade's Avatar
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    Default Re: Newbie to the forum

    Hi all

    just noticed a stupid mistake The CAN is running at 500Kb/s and not 512Kb/s. I checked my code for the other units and there it was. I've obviously caught age, probably a while ago at that

    Rob

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    Prolific Poster RGV250's Avatar
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    Default Re: Newbie to the forum

    Hi,
    I did not notice the error but it is still fast, are there any fantastically time critical things beig sent?

    Bob

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