Author Topic: Noob question isolating homemade programmer  (Read 5918 times)

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Offline Fixed_Until_BrokenTopic starter

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Re: Noob question isolating homemade programmer
« Reply #25 on: March 09, 2020, 04:14:52 am »
OK just tried holding the nano in reset by setting it to ground same issue.

here is a little picture of how it looks now I also went from a uno to a nano. I really appreciate the help. I have no background in this stuff I am just a dumb cop haha. I have already learned a ton from this project. 
 

Offline Ian.M

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Re: Noob question isolating homemade programmer
« Reply #26 on: March 09, 2020, 07:38:24 am »
OK just tried holding the nano in reset by setting it to ground same issue.
So, just to confirm, that was with the Nano properly powered and Nano ground connected to target ground? 

If not, please ignore the following, make it so and re-test.

I''ve just double-checked the ATmega328P datasheet to be certain I'm not misleading you:
Quote
15.1. Resetting the AVR
...
The I/O ports of the AVR are immediately reset to their initial state when a reset source goes active. This does not require any clock source to be running.
...
As all DDRx and PORTx registers are zeroed as their initial state, the I/O pins you are using for SPI *should* be tri-stated if the Nano is held in reset.  If /SS (your CS) isn't then either there's something wrong with your circuit or with that pin of the Nano.   Check that pin is floating with the Nano held in reset and no target connected (monitor the pin voltage with a DMM and see if it can be pulled both high and low with a 10K resistor alternately to Vcc and Gnd).

There is a small possibility its an AC loading effect caused by the extra capacitance of your programming cable and programmer circuit, that appears when the target accesses the memory becauuse its either got less drive or operates at a higher transfer rate (or both) than your programmer, so is more sensitive to load capacitance, however I would expect such trouble to be associated with the SPI clock or data lines not /SS, as they have far more frequent timing critical transitions than /SS.
 

Offline Fixed_Until_BrokenTopic starter

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Re: Noob question isolating homemade programmer
« Reply #27 on: March 09, 2020, 01:19:11 pm »
It was done with both powered on. I tested it again before I left for work just to make sure I did it right same issues. You are correct it's clock not chip select beer got to me on that one last night. I know chip select is pin 10. When I get home I will bust out the oscilloscope so we can see exactly what is happening to that clock signal.
 
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