This blog post continues upon yesterday’s post. In this post we will attempt to find the two missing serial console pins (RX and TX).
We will start with the TX (transmit) pin, this one is easy to detect, as most devices log their status during start-up. So, there are some high/low voltage bumps during start-up.
I will do this using a oscilloscope (I have a DSO nano pocket scope), although there are sveral other methods. One other (cheap) example is using a piezoelectric buzzer:
To use this buzzer you have to tie the black wire to ground, and connect/touch the suspected TX pin with the red wire. The piezo buzzer will then beep during start-up.
Let’s continue with the scope option though. Here’s a picture of my setup:
The ground clip from my scope is connected to another ground point I found using the continuity tester function, remember last post? The test clip from my scope is connected to one of the pins on the header. Hey, what are those waves on the scope display ?!
The waves we got is serial communication from the Belkin Home Base right to our scope! It actually took me 5 restarts of the Home Base. Pin 5 is our TX pin.
To locate our last pin (RX) we will first have to connect our Belkin Home Base to our PC. I use a USB-BUB for this. Any other FTDI cable will most likely be ok, i’ve also seen people use old telephone data cables for this purpose.
Here’s the USB-BUB with the Belkin Home Base TX pin connected to the BUB’s RX pin:
Great, so does it work? After fiddling around a bit with the baudrate/parity settings etc. I came up with the following settings:
Data bits: 8
Stop bits: 1
Here’s the result:
After it finished booting, I noticed the following:
Crap! It doesn’t allow us to login, so there is no way to test for the RX pin :-(
Normally I would just connect it to random pins and check if I can “type” to the serial console, unfortunately that’s not an option for this device.
To be continued…