Manually holding reset pin low during ISP

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I’m hobbying on a budget here and would like to program my ATmega328P using materials I already have: a MAX232, a null modem DE-9 cable and a real serial port.  I’ve been looking at using DASA through AVRDUDE, but it seems I need the DTR pin, which my specific MAX232 breakout thingy doesn’t have.  The main question here: assuming nothing goes wrong per the algorithm and /RESET need not be pulsed high, could I simply pull the reset pin to ground using a jumper cable and hook up the other pins accordingly?

my default username was taken so I used my real name lmao

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The DTR thing is only about Arduino and it's bootloader. The idea is that the PC (avrdude) has a way to control the AVR to say "you must restart now" and that gets it back to the bootloader so avrdude can "talk". The rather clever way they did this was to have an unused modem signal (DTR) coming out of the PC and connected to the _Reset system of the 328 so they could get a reset when they wanted it. But your thread title says "ISP". That is an ENTIRELY different thing - nothing to do with bootloaders, nothing to do with DTR resets and so on.

 

EDIT: actually if "hobbying on a budget" why not simply spend $5 and get an Arduino and spend the time having fun actually programming rather than trying to engineer some system to program the chips and losing a lot of hair in the process?

Last Edited: Wed. Oct 13, 2021 - 03:16 PM
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I don’t have a bootloader, no.  So, if I’m not mistaken, I can just connect everything but /RESET—which I manually hold low—and use the DASA3 option, right?

 

edit: It’s more that I live in a rural area and an Arduino Nano would take upwards of two weeks to ship here.  My initial rationale was that I’d be interfacing more directly with the MCU, and I like tinkering around with low-level stuff.

my default username was taken so I used my real name lmao

Last Edited: Wed. Oct 13, 2021 - 03:20 PM
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OK I was going to suggest a USBAsp (ie DASA about 2 decades later) but I guess you'd be looking at the same two weeks even if they are only $1 .. $2 on eBay.

 

If you have the bits to make a DASA (9 pin serial, MAX232 etc) then I'd go for it but forget al about DTR - that does not apply to you

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Welcome!

Seth Price wrote:
The main question here: assuming nothing goes wrong per the algorithm and /RESET need not be pulsed high,
There are two cases for de-asserted RESET.

Serial Programming Algorithm | AVR® Microcontroller with Core Independent Peripherals and PicoPower® Technology (mega328PB)

...

In this case, RESET must be given a positive pulse of at least two CPU clock cycles duration after SCK has been set to “0”.

...

If the 0x53 did not echo back, give RESET a positive pulse and issue a new Programming Enable command.

...

 

P.S.

Seth Price wrote:
but it seems I need the DTR pin, 
If current limit DTR then that may be acceptable (still an extremely brief over-volt); better is to level convert (pre-biased transistor)

 

P.P.S.

AVR Dx is the follow-on to megaAVR.

AVR32DA28 is in PDIP and in stock with a reasonable lead time.

Migration from the megaAVR® to AVR® Dx Microcontroller Families

Lead Time | World's Largest Inventory of Microchip Products

 

"Dare to be naïve." - Buckminster Fuller

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Seth Price wrote:
edit: It’s more that I live in a rural area and an Arduino Nano would take upwards of two weeks to ship here.
Is all up to two weeks?

Pololu's AVRISP (STK500v2) recently increased in price (+26%) so isn't as good a value versus USBasp though Pololu's does have more functionality.

Pololu USB AVR Programmer v2.1 (zero price USPS first class)

 

"Dare to be naïve." - Buckminster Fuller

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USPS First Class takes about that time, yeah.  I’ll look into that programmer, though; it seems pretty useful.

my default username was taken so I used my real name lmao

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Two week means nothing....five years from now you won't even know

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!