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Why does this CompactFlash to IDE adapter behave differently?

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First post, by Kahenraz

Posted on 
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* This is a copy/paste of a question that I made on Stack Exchange that was closed and automatically deleted. I've found it to be useful information for reference, and I'm reposting it here for my own record, as well as the benefit of others.

Cross-referencing other CF-IDE issues here:

Re: What retro activity did you get up to today?

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I have a pair of CompactFlash to IDE adapters. The one on the left works fine. The one on the right causes the BIOS to hang at startup, although it will eventually boot after several seconds. It also hangs when booting FreeDOS when it is running InitDisk, although it too will eventually reach the command prompt. The disk also detects fine in the BIOS.

I have tried several different CompactFlash cards with the same result. The adapter on the right consistently causes problems.

These are passive adapters. The only difference between the two that I can see is that the one of the left uses a single resistor, while the one on the right is a resistor package and two A2 NPN transistors.

What is the difference between these two adapters that might be causing this problem?

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Reply 1 of 2, by DerBaum

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It seems like the 2 components interact with PIN39 wich is the DASP Pin to select Master/Slave .

The computer determines if there is a second (slave) drive attached through the use of Pin 39 on the connector.
Pin 39 carries a special signal, called Drive Active/Slave Present (DASP), that checks to see if a slave drive is present.

https://computer.howstuffworks.com/ide.htm

On the version with the 2 components the master/slave jumper has 2 Pins, and on the other one without these components the jumper has 3 pins.

My best guess is that these 2 components pull the pin high when the jumper is not set, and the jumper sets this pin low (or the other way around).

On the other version with the 3 Pin Jumper you probably set high/low with just the position of the jumper.

But thats only a quick guess...

FCKGW-RHQQ2

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