Tiny4313 and INPUT on PIN D5

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Hi,

I have small display and it is controlled by AT89C2051, Now I have to change firmware and would like use AT-Tiny4313 (it is pin compatible with 89C2051 (except RESET)). When I wrote SW and connect Tiny4313 to display after approx 20sec broke PIN D5. I am using it like INPUT with internal PULL-UP. It is broken that, it is not working like input and it is permanently in LOW, no chance PULL-UP it externally - I have tried it. When I try change status to OUTPUT and change port value LOW-HIGH-LOW-HIGH-... it is working. When I connect signal from D5 to another pin like D6 or D4 - it is working without problems.

- Note: I thing, there is not problem with my connection because another ports has the same external connections, but only D5 has this problems. I have tried connect 2 TINYs4313. And the both has the same fault.

My question: D5 is has different electrical characteristics?
Has anybody the same exprience?

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You know that changing the RESET pin to an IO pin has to be done clearing the "Reset disable" fuse ?
and as such you can no longer re-program your AVR using an ISP, but have to use high voltage programming?

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RESET pin of as 4313 is PA2.

What have you connected to PD5 ?

Can high voltage or current get to this pin?

Changing 89C to Tiny should be trivial. Remove the massive capacitor on RESET. Remove the pull-down resistor. Possibly use a 10nF capacitor and external pull-up on RESET.

Since your 89C hardware expects 8051 output pins, you may use 4313 in 'open drain' output mode instead of 'push-pull'.

David.

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I have not problem with replacing 89c2051 by T4013. When I connect signal instead PD5 to PD6 - everything working good. But I have to replace CPUs on approx. 100 devices - and, it is impossible on every PCB make HW changes. (PD5 -> PD6). I have to replace DIP 89C2051 by DIP AT Tiny4313 and remove Reset capacitor, no more.
- signal way is GND - BUTTON - RESISTOR - PD5. Important is PD6, working. PD5 not. Unfortunately I need PD5 - murphy's law.

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Never heard about such failure. I know you expect a silicon bug, but "after approx 20sec broke PIN D5" indicates that the chip was trying hard..
I suggest you should check:

    1. if you do not violate specification - mount a U~VCC Zener at your pin for now just to verify a voltage (applied externally) does not exceed VCC at some moment. Will it survive longer than 20s? 2. Next thing is that this pin is next to GND pin. Any shorts? Open circuits?
    3. Then there is a PUD bit which disables internal pull-ups globally. I know that this crappy OCD cannot break at such write easily, so I suggest a temporary 1Mohm pull-down on pull-uped pin (i>1uA). It will not disturb a pullup to operate as expected but will instantly force a pin to GND if pull-up is accidentally removed. A DVM (or better a triggered scope) there could verify if internal pull-up works ok.

No RSTDISBL, no fun!

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Never heard about such failure. I know you expect a silicon bug, but "after approx 20sec broke PIN D5" indicates that the chip was trying hard..
I suggest you should check:

    1. if you do not violate specification - mount a U~VCC Zener at your pin for now just to verify a voltage (applied externally) does not exceed VCC at some moment. Will it survive longer than 20s? 2. Next thing is that this pin is next to GND pin. Any shorts? Open circuits?
    3. Then there is a PUD bit which disables internal pull-ups globally. I know that this crappy OCD cannot break at such write easily, so I suggest a temporary 1Mohm pull-down on pull-uped pin (i>1uA). It will not disturb a pullup to operate as expected but will instantly force a pin to GND if pull-up is accidentally removed. A DVM (or better a triggered scope) there could verify if internal pull-up works ok.

No RSTDISBL, no fun!

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I have checked it again . But nothing new. In this time I have not any new Tiny. I have to wait for Farnell delivery. Your idea with 1MOhm pull down resistor is important. ( I forgot - zener diode is close input connector.)

Thanks all for your ideas. I think, if nobody has experience with this problem - It is mean that I have to check again all HW around my CPU.

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Quote:
It is mean that I have to check again all HW around my CPU.

Almost guaranteed!

Charles Darwin, Lord Kelvin & Murphy are always lurking about!
Lee -.-
Riddle me this...How did the serpent move around before the fall?