I've seen these before, you're going to have to break out the soldering iron and magnifying glass. The dumbasses who built them connected +5V to pin #4 on the IC, which is the pull-up voltage for the serial lines (and is only spec'd to be in the range of 1.8V - 3.3V, they're lucky the chip isn't fried). So you have to lift pin #4 and connect it to 3.3V (e.g. pin 17) to make it properly run at 3.3V.

(Unless you can see a bridge or similar on your board that would let pin #4 connect to 3.3V instead of 5V...)

jmarsh wrote on 2024-06-05, 20:03:

I've seen these before, you're going to have to break out the soldering iron and magnifying glass. The dumbasses who built them connected +5V to pin #4 on the IC, which is the pull-up voltage for the serial lines (and is only spec'd to be in the range of 1.8V - 3.3V, they're lucky the chip isn't fried). So you have to lift pin #4 and connect it to 3.3V (e.g. pin 17) to make it properly run at 3.3V.

(Unless you can see a bridge or similar on your board that would let pin #4 connect to 3.3V instead of 5V...)

Will an 0.2mm copper wire be enough for 3.3v? Also, measuring the 3.3v pin (next to 5v, Tx and Rx) I get 3.4v. That should still be in spec for 3.3v line right?

(baffled by the decision to just over-volt the logic, rather than incorporate a level shifter into the design.)
(Further baffled that they decided to drive logic levels at 5V on a TTL serial cable, since nothing modern will want to talk at 5V levels.)

---[While I understand that "Cost savings!!" was the likely motivator, trying to drive ANY of the devices you would want to connect this to at 5V will likely fry the UART on the other end!! Why even BOTHER pushing 5V?! This is NOT a 9pin serial cable with 5V logic!!]--

(Thinks it would have been much more intelligent to add a few transistors and resistors to have a 5v level shifter, and a single position DIP switch to select mode that turns it on or off.)

I've connected it to 3.3v pin near Tx and Rx and it works! I didn't fry anything, but Rx is 3.6v, so its high, but it still should be ok for 3.3v devices, right? Tx is 3.34v, so pretty spot on. Any ideas if this won't cause damage?

3.6v should be in expected tolerance for 3.3v TTL. It should be fine.

wierd_w wrote on 2024-06-06, 10:31:

3.6v should be in expected tolerance for 3.3v TTL. It should be fine.

Thanks for the quick response. And another question, do I also need to connect GND pin to the device on the other end? I'm connecting it to an Seagate drive from an gen 1 xbox (sold the xbox and only left the disk).

It's necessary for gnd to be connected, to get data on the rx line.

Yes.

If you are trying to get rid of the ata-lock status, certain gen1 xbox drives will 'forget' their lock status after a firmware update (which they will accept, even when locked.)

It's best to hot-swap the drive after being powered on by the xbox, and then told to clear the lock status with hdparm, though.

But... you sold the xbox...

wierd_w wrote on 2024-06-06, 15:06:

It's necessary for gnd to be connected, to get data on the rx line. […]
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It's necessary for gnd to be connected, to get data on the rx line.

Yes.

If you are trying to get rid of the ata-lock status, certain gen1 xbox drives will 'forget' their lock status after a firmware update (which they will accept, even when locked.)

It's best to hot-swap the drive after being powered on by the xbox, and then told to clear the lock status with hdparm, though.

But... you sold the xbox...

Connected the GND pins, but I'm still not getting anywhere (PuTTY freezes on the green cursor). Oh well. Guess thats for another topic.