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Powering CF to IDE adapters

Rauli

Experienced Member
Joined
Sep 16, 2013
Messages
114
Location
Spain
Looking for a CF to IDE adapter, to replace an old hard disk in an old computer with a CF card, I have discovered a variety of models: With or without bracket (to instal in the back side of the PC), with male or female connector, with the connector straight at the edge of the card or at a right angle, single or dual, with or without master/slave jumper AND (the subject of my question) with or without a voltage jumper and with or without a 4-pin floppy-like power connector.

What's the story with this jumper and the power connector? The jumper (if exists) let's you select between +5 and +3.3V, but, when does somebody need to select +5 or +3.3? Does it depend on the computer? On the CF card? On what?

And 2nd, some adapters have the inscription "Autoselect power supply (IDE pin 20 or external)". How does this autoselection works with the voltage jumper? Does the jumper select voltage only for IDE pin 20? Only for external? For both? I'm supposing that "external" means the floppy power connector, but I'm not 100% sure.

Also, I have tried one of these with the "autoselect" feature, and without voltage jumper. But on my modern PC it only works if I plug the floppy power connector. So, is this feature one of those things which almost never works? Or is it something which uses to work and I'm just being unlucky?

PS: Sorry if there was a better forum for this, but I think it's neither Vintage Computer Hardware nor Vintage Computer Tools and I couldn't find a better place.
 
Pin20 power must be supplied by the host for that to work. It will be 5V.

All CompactFlash cards are required to support 5V or 3V3 operation, and CompactFlash is a CMOS based technology. Therefore 5V should be used in very old machines pre-dating (from memory) ATA-3, since these use 5V TTL logic. ATA-3 and later use 3V3 logic, which would not be compatible with 5V CMOS logic levels.

These adapter cards generally have diodes to drop the voltage to 3V3 usually from the 5V provided by the floppy header or Pin 20. Some of the adapters I have seen unfortunately also keep a diode inline with the Pin20 power, and therefore can cause data integrity issues.
 
Some of the adapters I have seen unfortunately also keep a diode inline with the Pin20 power, and therefore can cause data integrity issues.

Could you elaborate a bit on this? Sounds like a good thing to know in order to avoid potentially problematic adapters...or maybe to just somehow modify them to bypass the diode?

Thanks,

Wesley
 
I'd say the extra diode causes an extra voltage drop so <5V is present on Pin 20 (or < 3.3V if present).
 
Correct, I measured about 4.4V at CompactFlash Vcc I think. Simple answer is to power the adapter via floppy Molex.
 
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