Originally Posted by yifanlu
I don't know why you made a new thread when I just wanted a one sentence answer from someone, which is why I asked in the IRC and not on here (it's like I texted you and you sent your reply via snail mail, if you do this for every question I ask, there will be a lot of new theeads), but never mind that.
I did read that post you linked to a while ago and I asked because I want to make sure of the "bottom" and "top". Can you reference other components like "top below X" and "bottom above Y"?
And since we have a thread going, let's not waste the space. Anyone want to share how they connected the USB serial? Do I need an external power supply running 1.8V? Any specific adapter that works "out of the box"? I have a 3.3V USB ttl adapter that worked on the K2. The chipset supports 1.8V, but the adapter has jumpers only for 3.3V and 5V. Also, I was too cheap to buy a new soldering iron and my old one is very worn out so any way I can check if I soldered everything correctly and no shorts over the pads, I mean it boots and my multimeter doesn't show a connection on rxd->txd or txd->gnd and it got 1.8V successfully.
Hmm... I thought we were done with hostile criticism of each other's posts. I guess not...
I misplaced my camera, or I would have have posted a photo just for you, with clearly labelled pins. In lieu of that, I took comments from my old buried post that already described the pins, and I created a new thread where it would be easy to find, and I added more text to be sure you would understand the pinout and the possible need for level shifting.
Then because I thought you might not actually read all of it, I added a one-line summary at the top. I even labelled the one-line sentence as "Short version".
And I went into great detail about getting 1.8v working with my super simple level shifter circuit. After I kept getting questions from my various posts, I started a new thread on that too.
I went to great lengths to try to avoid all misinterpretations and false assumptions that could be made from the short version, but ALSO explaining it at great length.
In every post about serial connections, I clearly stated that a REAL 1.8v adapter such as seaniko7 suggested is the preferred solution, but I keep getting replies that the ones from distributors cost too much (typically $25 USD plus shipping).
The one you have should work fine IF you remove its TxD LED (if it has one). If you use a 22K resistor like I did to connect the supply voltage to the level shifter circuit, it does not matter whether the supply voltage is 3.3v or 5v.
As shown in my other posts, 3.3v and 5.v TTL use exactly the same logic levels, and 1.8v TTL is different. Although many adapters need level shifting, some are more tolerant and work right out of the box.
Or, you could just do it the way I did and examine the signal at the pins. While booting, the middle pin showed a stream of pulses on the middle pin that looked like data bits, when the scope ground was connected to the metal battery cover. The top pin that looked different from the others measure zero ohms between it and the battery cover, so it was GND.