Programming RSTDISBL on an Attiny48 via ISP?

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I know that I need the reset signal to program via ISP and according to the datasheet... I can program fuses via ISP.  Can I program RSTDISBL using ISP?  If it were at all possible, I assume it would be the very last thing you would want to program as once you do it.... ISP ability is lost.  Just not sure if programming RSTDISBL via ISP was possible at all. 

Thanks,

-Adam

-Adam
"Please don't judge my God by my inability to follow him" - Chris Mollins
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www.onecircuit.com
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ajcrm125 wrote:
Just not sure if programming RSTDISBL via ISP was possible at all.

Yes, it is possible.

 

But think long and hard about the ramifications.  After you sail your course, you cannot reset your device with external reset.  And any reprogramming is problematic, especially with a surface mount chip.

 

Yes, there are experienced 'Freaks that have done it.  The general answer here is "don't".  Another response is to tell you I/O, and perhaps someone can come up with a way to get "one more I/O".

 

Also consider a couple side effects.  From memory, you won't have protection diodes on that signal.  And on at least some models, that I/O won't have normal drive.

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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Yes,  of course you can program RSTDISBL via ISP.    Members do it frequently.

 

You can also shoot yourself in the foot.

You can bang your head against a wall.

You can step in front of a bus.

...

 

The ATmega48 has a reasonable number of pins.   I would do everything to avoid RSTDISBL.    There are many tricks to share pins or do multiple things e.g. Charlieplex.

 

David.

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The ATmega48 has a reasonable number of pins

OP spec'd ATtiny48, but yes same number of I/O.

 

Restoring /RESET will require HVPP and 21 signals, including 12V on /RESET, plus VCC and GND.

 

There are many tricks to share pins or do multiple things e.g. Charlieplex.

Another response is to tell you[sic] I/O, and perhaps someone can come up with a way to get "one more I/O".

+1.

"Experience is what enables you to recognise a mistake the second time you make it."

"Good judgement comes from experience.  Experience comes from bad judgement."

"When you hear hoofbeats, think horses, not unicorns."

"Fast.  Cheap.  Good.  Pick two."

"Read a lot.  Write a lot."

"We see a lot of arses on handlebars around here." - [J Ekdahl]

 

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joeymorin wrote:
OP spec'd ATtiny48, but yes same number of I/O.

Let's poke at that for a moment. ;)  OP hasn't seen fit to tell us the package.  Nor clock source.  For Tiny48:

 

For Mega48:

One still needs to read between the lines a bit...

 

For us normal people, a Mega48 [always] has:

 

8 I/O PD0-PD7

6 I/O PC0-PC5

6 I/O PB0-PB5 which adds up to 20.

 

Add PC6 (RESET) and PB6/PB7 (XTAL1/XTAL2) and a total of 23.

 

However, the 32-pin packages have ADC6 and ADC7.  While not GPIO they can easily be pressed into service to e.g. read a couple of switch inputs. 

============

Looking at the Tiny48 in 28-pin packages the counting needs to be done differently.  There is no AREF, so there is always PC7.  There is no crystal, so there is always a PB7.  PB6 can be CLKI.

 

On the 32-pin packages we pick up PA0 and PA1, turning ADC6 and ADC7 into "real" pins.

 

I'll let you do the totals, but Tiny48 does pick up one or more I/O pins at the expense of other functionality.

 

joeymorin wrote:
response is to tell you[sic] I/O,

Indeed, my fingers often change the intended your to you.  Sometimes I pic it up before someone has the opportunity to make a sic comment.

[typo deliberate; close to a pun...]

 

 

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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Do folks really need a 29 pin chip? cheeky

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RSTDISBL was an early attempt by Atmel to sell more chips, in more ways than one.

When in the dark remember-the future looks brighter than ever.