PS2 optical mouse - brand unknown.

The 12-pins IC (integrated to the camera) is an ATL A2188 for which I found no datasheet in the Web.

Checked the rotary encoder used for the scroll wheel: mechanical switches with detents.

After probing its terminals with a scope, I realized that each switch brings in turn, in ON / OFF sequence its respective pin to ground.

Also the 3 microswitches (left - right - wheel) do exactly the same, bringing their respective pins to 0V when pressed down.

My question: the pull up "resistors" inside the IC, what are they? Common resistors or active transistors?

Additional (not related to the above): in the waiting state, the LED is driven permanently with a 6% duty cycle. For full brightness DC becomes 100%. Frequency is 96 Hz.

The sole resistor used in this mouse goes in series between the +5V and the LED.

 

Thirty years ago, I read that resistors take up a lot of space on an integrated chip, so the usual way was to use a jfet pretending to be a resistor.

This is VERY OLD information.

 

This is VERY OLD information.

So? Should I beg for pardon #12? Are you becoming intolerant? Hope not YOU, precisely.

 

No. I'm telling you not to trust what I said because that method was popular 30 years ago. It might not be true today.

 

More likely he means that he doesn't know if that's still the way they do it.

 

Here's a quote from a data sheet from the current decade:

The integrated weak pull-ups consist of a semiconductor structure similar to, but somewhat different from, a discrete resistor.

Well THAT certainly clears it up.

 

No. I'm telling you not to trust what I said because that method was popular 30 years ago. It might not be true today.

Now I understand.

SORRY for my reaction. You do not deserve that!

 

Here's a quote from a data sheet from the current decade:

The integrated weak pull-ups consist of a semiconductor structure similar to, but somewhat different from, a discrete resistor.

Well THAT certainly clears it up.

Well slap my MOSFET and feed me a diode, that explained EVERYTHING.

I wish these data sheets could be a little more specific, I haven't found anything better either...

 

Now I understand.

SORRY for my reaction. You do not deserve that!

This kind of behavior makes me suspect you are married.

 

Thirty years ago, I read that resistors take up a lot of space on an integrated chip, so the usual way was to use a jfet pretending to be a resistor.

This is VERY OLD information.

I don't know what exact device this came from but, it the numbers on the chip are a date code instead of a part number, #12 was not too far off with "30 years ago" comment.

ATL A2188 >>> week 21 1988.

Could your part be some type of shift register or serial interface chip. It could take the current state of the encoder and switches as inputs and send the put to the interface as a serial signal. It would explain why each button press ore wheel turn changes a pin voltage.

 

This kind of behavior makes me suspect you are married.

...STILL married!

 

I don't know what exact device this came from

PS2 optical mouse, mentioned in the title of the thread.

ATL A2188 >>> week 21 1988.

The IC handles the whole thing inside the mouse, which is optical and did not exist in 1988. I fear the designer of the chip was still in college in 1988.

It is mentioned in the Web at many sites but no datasheet while those with less pins (8?) seem much more common and available. More recent?.

 

It simply means that there are internal pullup resistors. The details of how they are implemented are unimportant to the question of their existance.