In need of logic gates

[reaper57]

Hi! I am trying to do a project, but I am unable to find the names (and therefore models) of the types of logic gates that I need.
No1:
What I want it to do is bridge two of the pins together whenever there is voltage on a third. However, I don't want it to output the "enable" voltage through any of the other pins.
No2: I want this one to be the opposite of the first one. I want the two pins to be bridged if a voltage is NOT present on a third.
Basically, what I want to do is connect a USB port to the motherboard, whenever an S0 voltage appears, but disconnect it (and connect it to something else), when the system is in an S5 state and there is no current on the S0 rail I'm using for a reference.

[eccerr0r]

Re: In need of logic gates

This is a bit more than just "logic gates" as "bridging" two pins together isn't necessarily a logic function. You'll need to know what voltages we're talking about first - what if it's hundreds of volts that needs to be bridged? May need a thyristor + optocoupler or relay or something. Usually the relay or relay and a transistor are a safe bet.

The S-states may not be directly visible on the USB port, unless in S5 the USB ports do not pass out +5VSB... Then it's a bit easier.

[stj]

Re: In need of logic gates

logic gates dont "bridge" anything,
the output goes high or low based on input states.

[reaper57]

Re: In need of logic gates

logic gates dont "bridge" anything,
the output goes high or low based on input states.

Then what do I need?

[reaper57]

Re: In need of logic gates

This is a bit more than just "logic gates" as "bridging" two pins together isn't necessarily a logic function. You'll need to know what voltages we're talking about first - what if it's hundreds of volts that needs to be bridged?

As I said, a USB port. Data +, Data - and +5V. So nothing more than 5V 500mA. As for the reference voltage, it's going to be 2-5V.

[budm]

Re: In need of logic gates

If I read it correctly, when S0 voltage appears you want D+, D- lines to be connected to the mother board, and when S5 state is present, you then want the D+, D- lines to be disconnected from mother board as if you have removed the device from the USB port.
Is that correct?

[stj]

Re: In need of logic gates

cant be done wih standard logic, usb is bi-directional.

[reaper57]

Re: In need of logic gates

If I read it correctly, when S0 voltage appears you want D+, D- lines to be connected to the mother board, and when S5 state is present, you then want the D+, D- lines to be disconnected from mother board as if you have removed the device from the USB port.
Is that correct?

Exactly! Same goes for the +5V as well.

[stj]

Re: In need of logic gates

you can just kill the 5v - there are chips for that used in laptops.

[reaper57]

Re: In need of logic gates

you can just kill the 5v - there are chips for that used in laptops.

I don't want to kill it as I need it to be present when the board is powered on. Also, an external device will be providing power to the USB when the board is off, and I don't want it to be back feeding.

[stj]

Re: In need of logic gates

what is the usb device?

[reaper57]

Re: In need of logic gates

what is the usb device?

Not sure why it matters, but I'll explain everything I'm trying to do here.
I want to permanently install an SPI nand flasher in a 360 console. Thing is, the flasher would fry itself if connected to the board when it's powered on. So I want to break the connection when a S5 voltage is present. Now onto the USB part. I don't want to have cables and hot glued ports sticking outside of the console, instead I want to use one of the USB ports on the motherboard. So, I need to break the connection to the board when the board is off and instead connect it to the nand flasher. Then when the board is powered on, I want to use the same method to disconnect the nand flasher from the board and the USB port, and connect the USB port to the motherboard.

[stj]

Re: In need of logic gates

then you really need a 3pco relay with a 5v or 12v coil and a logic-level fet to switch it.
maybe a BS170

it wont be simple, usb requires both wires to be exactly the same length for example.

but will it still be o.k. with the other side of your flasher permanently wired to the flash?
some wiring schems would be good.

[reaper57]

Re: In need of logic gates

but will it still be o.k. with the other side of your flasher permanently wired to the flash?

No, as I said the flasher will get fried if left connected after the board is powered on. So, the flash too needs to be disconnected when the board is on.

some wiring schems would be good.

usb requires both wires to be exactly the same length for example.

Everything will be mounted close to the port, so that won't be an issue.

then you really need a 3pco relay with a 5v or 12v coil and a logic-level fet to switch it.
maybe a BS170

Sooo, I looked at the datasheet and this is what I made out of it:
If I connect one of the USB pins to VDGR and connect the board side to VDSS, the two should get bridged together when I apply voltage to VGSS, right?
Also, thank you for the help so far!

[stj]

Re: In need of logic gates

no, i meant use the fet as a current booster to switch a 3 pole relay.
use the relay to switch the vcc and D+ / D-

[reaper57]

Re: In need of logic gates

no, i meant use the fet as a current booster to switch a 3 pole relay.
use the relay to switch the vcc and D+ / D-

Why would I need a current booster?
Sorry, if this sounds stupid, but it's my first time "designing" something like this.

[reaper57]

Re: In need of logic gates

Also, how would I go about disconnecting the flasher when the reference S5 voltage appears?

[stj]

Re: In need of logic gates

the relay coil uses too much current to drive directly from a logic signal.

[reaper57]

Re: In need of logic gates

the relay coil uses too much current to drive directly from a logic signal.

What if I use the 12V coming from the PSU? They are only present when the console is on.
Also, if you read this post in your email (before I edited it), that was auto correct.

[stj]

Re: In need of logic gates

you could do that.
but where does the flash chip get power when that programmer is doing it's thing?