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[wxsig] Programming/Communicaton Problems

David skyhammer at gmail.com
Fri Mar 24 16:09:16 UTC 2006


Hi Will,

Thank you for your helpful suggestions.  I ordered the 9.8304MHz 
oscillator from DigiKey, rigged up a little board with some jumpers, and 
inserted it as per the original T238 schematic.  It isn't pretty, but it 
did the trick, and I successfully programmed the CPU...or at least I 
think I have.

You mentioned about performing a "clean reset" to the CPU;  I tied the 
IRQ pin of the CPU to pin 2 of the MAX232 (V+), is this OK?

I'm still having some other problems though.  In particular, the LED 
does not flash, and I have no display.  I'm fairly certain I've 
eliminated all the usual suspects:  solder bridges, broken traces, 
component polarity, etc.  I have also checked the clock, and have 
verified this with a 'scope and checked the output pin (pin 4) of the 
CPU too.  Since there is not much else between the CPU and the LED 
itself, I was wondering if I had indeed programmed the CPU correctly; I 
don't know if the software will have any direct effect of the LED or 
not, so I was hoping you might have some thoughts on this.  At the 
moment, the LED's state is always on, and there's about 2V supplying 
it.  If I connect a 'scope to pin 21, there doesn't appear to be any 
pulsing, as one might expect.

Thanks again,

David

Will Beals wrote:
> David:
>
> Cool on building your own board.  To get the P&E tools working, you need
> remarkably little external support.  To get it to work, you need to ensure
> that your board is following all of the requirements in Section 15 of the
> MC69HC908GP32 Technical data manual.  In there is the schematic of all the
> hardware needed which I (mostly) copied in the T238.  The only place I
> really strayed from their suggested schematic was replacing the 74HC128 IC
> with a single schotkey diode (kind of proud of this myself).  Of particular
> note, make sure all the pullup and pulldown resistors on Port A bits 0 and
> 7, and Port C bits 0, 1, and 3.  I have pullups and pulldowns on there to
> get the chip to boot into the right state for P&E tools if the CPUs IRQ line
> is pulled high to Vtst (I get Vtst from the MAX232).  Other than that, all
> you should need is +5V and the 9.???MHz clock.
>
> Finally, make sure you issue a clean reset to the CPU.  That is harder than
> you think.  If you are tying IRQ to VTST, you end up back-powering the CPU
> through Vtst.  My solution was to have the RESET button actuall actively
> pull VCC to the CPU down through a 10 ohm resistor.
>
> That should really do it.  I'm hoping you missed one of those resistors I
> had in the T238 thinking it was for another purpose or something.  If you
> are still having trouble, let me know.
>
> will
>
> -----Original Message-----
> From: wxsig-bounces at lists.tapr.org [mailto:wxsig-bounces at lists.tapr.org] On
> Behalf Of John Koster
> Sent: Monday, March 20, 2006 11:47 PM
> To: TAPR Weather Station SIG Mailing List
> Subject: Re: [wxsig] Programming/Communicaton Problems
>
> OK, now it makes sense.  You would have been better served to have followed
> the classic T238 schematic.  All the pieces would have been in place to
> program your MCU from scratch.  That's the platform used to program the
> chips we put in the T238+ kits.  
>
> I'm sure Will can chime in here later to give you better advise.  
>
> --
> 73,
> John, W9DDD
>
> On Tue, 21 Mar 2006, David wrote:
>
>   
>> Hi John,
>>
>> I am building the board from scratch, so my PCB layout for the traces 
>> are not the same.  However, the general layout of the components are.
>> Since I do not have a pre-programmed MCU, I need to program it myself, 
>> presumably using the P&E toolset.  I have downloaded the latest 
>> software
>> (1.15.8) from http://www.beals5.com/wx/ - This is also the same place 
>> that I downloaded the manuals, schematics, etc., from.  The bottom of 
>> the assembly manual states:  T-238+ Assembly Manual, Rev. 2.1 November 
>> 2005, and the operations manual states:  T-238+ Operations Manual, Rev.
>> 2 April 2005.
>>
>> Software development would be something I'd consider in the future, 
>> but for the time being, I'd just like to program the MCU without 
>> having to buy a programmer.
>>
>> Many thanks,
>>
>> David - VA7DMS
>>
>> John Koster wrote:
>>     
>>> Are you trying to do software development, or just load the lastest 
>>> revision of the T238 software?
>>>
>>> Also did you download the correct assembly manual?  Otherwise I 
>>> don't understand the comment about the board not being identical?
>>>
>>>
>>>   
>>>       
>> _______________________________________________
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>> https://lists.tapr.org/cgi-bin/mailman/listinfo/wxsig
>>
>>     
>
>
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