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Thread: 40 Pin IDE / 39-Pin + 1 Empty - Same?

  1. #1
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    Default 40 Pin IDE / 39-Pin + 1 Empty - Same?

    Just want to verify that the 40 Pin IDE connectors and the 39-Pin (with 1 empty pin slot) work the same....

    I am going to build another Compact Flash ISA Adapter and the IDE Connector I have right now is a 39 + 1......
    "In Life, The Days Are Long But The Years Are Short..."

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    That key pin is not used by HDDs, but it can be used as 5V power supply to connect CF or a disk-on-module in some scenarios, IIRC. I don't know if your board actually has that connection or how you planned to connect CF to the 40-pin header.

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    Quote Originally Posted by bakemono View Post
    That key pin is not used by HDDs, but it can be used as 5V power supply to connect CF or a disk-on-module in some scenarios, IIRC. I don't know if your board actually has that connection or how you planned to connect CF to the 40-pin header.
    I have a motherboard that was missing pin 20 in the IDE Headers. Since I wanted to use DOMs for HDDs and didn't want to use external power connection, I added the missing pin to both headers and soldered a jumper wire to supply 5V on the back side of the board. Works perfectly and wasn't difficult.

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    Quote Originally Posted by bakemono View Post
    That key pin is not used by HDDs, but it can be used as 5V power supply to connect CF or a disk-on-module in some scenarios, IIRC. I don't know if your board actually has that connection or how you planned to connect CF to the 40-pin header.
    That pin #20-for-power thing is kind of an informal "Industrial PC" hack that's not actually part of the ratified IDE standard. If you have an older desktop PC that has an IDE plug with pin #20 present it's probably just not connected to anything. Manufacturers were pretty inconsistent about leaving that pin out at least until the middle/late 1990's.

    So, yeah, the short version is *most* of the time it makes no difference if the pin is there other than having it on your XT-IDE card might frustrate trying to plug in some cables. But if you intend to direct-plug a CompactFlash adapter or DOM having it there with +5v on it can save you a power cable connection.

    The first version of an XT-CF card I built for my Tandy 1000EX included the 5v-on-20 thing and it works fine for powering a CF card adapter that has support for it. For later versions I've switched to putting a 44 pin laptop plug on them to directly support a PATA-to-SD widget that seems to reliably support the necessary 8-bit transfer mode.
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  5. #5
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    The card will be connected via CF Adapter that has a Floppy Power Cable.....so I think it will be OK with the 39 Pin adapter.

    Thanks for verifying this for me!
    "In Life, The Days Are Long But The Years Are Short..."

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