go_away

Author Topic: Testing for Internal pull-up/down resistor  (Read 1754 times)

0 Members and 1 Guest are viewing this topic.

Offline krichTopic starter

  • Robot Overlord
  • ****
  • Posts: 165
  • Helpful? 0
Testing for Internal pull-up/down resistor
« on: January 13, 2008, 10:46:29 PM »
Not exactly robot related, but here's my situation:

I've got an unknown IC with an array of 8 input pins (suspect its an IDS1100 or 1200 series, pins A0-A7).  Two of them have built in pull-up resistors, the rest have built in pull-down resistors.  The problem is that this is not the DIP form, its the die form.  I can get to the pins (barely), but I don't know which pins are which.  I just need to separate those that are high from those that are low.

Looking at the schematic on the datasheet, I'm thinking that I can test this with a continuity test to either the Vcc or GND rails without powering on the chip.  Is this true?

If I need to power the chip to test it, what's the safest way to test?  I don't want to inadvertently smoke the chip.  Are these the results I should be looking for?

Voltmeter readings, testing from the pin in question to:
Test to GND, get 0v, this is a Low pin
Test to GND, get Vcc, this is a High pin
Test to Vcc, get 0v, this is a High pin
Test to Vcc, get Vcc, this is Low pin

This is probably pretty basic, but I'm still green at this and I only have one of these chips and I can't replace it.

Thanks for your insight.


Offline paulstreats

  • Supreme Robot
  • *****
  • Posts: 1,381
  • Helpful? 21
Re: Testing for Internal pull-up/down resistor
« Reply #1 on: January 14, 2008, 01:27:38 AM »
Quote
Looking at the schematic on the datasheet, I'm thinking that I can test this with a continuity test to either the Vcc or GND rails without powering on the chip.  Is this true?



Get a multimeter with a continuity setting (it beeps if the circuit is true) - generally has the picture of a musical note plus a picture that looks like the symbol for a diode.

Select continuity mode on your meter and touch the probes togethr, you should hear a beeping sound.

Touch 1 to gnd on your IC and test the pins with the other, if you hear the beep then the pin has a pull down resistor.

-----------------------

You can also do this with the ohm meter (resistance checker) that is a standard part of multimeters, set it to around 20K and touch 1 probe to gnd and test the other pins with the other probe if the screen shows a resistance value it is likely that the pin has a pull down resistor

Offline krichTopic starter

  • Robot Overlord
  • ****
  • Posts: 165
  • Helpful? 0
Re: Testing for Internal pull-up/down resistor
« Reply #2 on: January 14, 2008, 02:14:30 AM »
Thanks Paul.  I guess I needed moral support more than anything.  Turns out that the IC is a IDS1200, no internal resistors at all.  Additionally, all 8 pins were tied together and then to ground (all this happening very near or under the die, I think).  Short version of the story, I've figured out that there's no way I can get to the addressing features of that chip with how they have it set up.  I destroyed the die trying to separate the pins.   :-\

It was one of those voice recorder picture frames with a message from my daughter when she was 5.  The record button inadvertently got pressed this afternoon, just for a split second.   After doing research, I found that the device is like a cassette tape.  The recording is still on the chip if its not been recorded over.  If they had used a DIP rather than a die, I know I could have saved it.   :'(

Such is life in the digital age.  On the bright side, she's only 10, so I had better go find another frame and get her to record another message before she gets any older.  Also, I've learned quite a bit about these Single Chip Voice Record/Playback Devices.  I'm just going to have to think of a way to integrate that into my projects.   ;D

Cheers,

Ken.

 


Get Your Ad Here