I've purchased a used Raspberry Pi and have followed the instructions from Wolf Paulus's Journal to connect to the Raspberry Pi from my computer using a PL2303 USB adapter. The specifications on the PL2303 adapter say that it is for use with 3.3 V devices such as the Raspberry Pi.
Sending data to
/dev/cu.usbserial and watching the voltages on the TX and RX confirms that the maximum voltages are right around 3.3 V - so I believe the adapter is good and that it is connected to the three correct pins (common ground, no connection with the red +5 V wire).
When I boot the Raspberry Pi I'm not getting any console messages via the serial device even though I'm using the default Raspbian image. I've tried
/boot/cmdline.txt with both
console=ttyAMA0,115200 (default) and also
console=ttyAMA0,115200 kgdboc=ttyAMA0,115200 as was suggested elsewhere, but I get nothing.
When I run
stty -F /dev/ttyAMA0 I get:
speed 115200 baud; line = 0; -brkint -imaxbel
Other than purchasing more of these and swapping them around, how can I test the Raspberry Pi to see if the serial / UART is good? And how can I test the PL2303 USB cable to see if that is good? Are there low-level tests I can do? Or perhaps something with an oscilloscope?
Additional information per @joan's request:
- The USB is connected to the computer
- I have tried connecting with 115200, 38400, and 9600 bit/s
- I'm not even getting strange characters to indicate that the baud is incorrect
- On the computer I'm using screen to connect:
screen /dev/tty.usbserial 115200 8N1
/dev/cu.usbserialare the devices for this USB adapter
- On the Raspberry Pi I'm using a stock
2014-09-09-wheezy-raspbianimage which has "Enable/Disable shell and kernel messages on the serial connection" set to "Enabled" (default setting)
- The pins are connected to the Raspberry Pi like this. I have tried switching white / green "just in case", but without luck either way:
I believe I'm doing everything correctly so my question is more about how to know if there is either a problem with the USB adapter or the Raspberry Pi's serial connection.
Also, I was also curious if there was a way I could use
screen on the Raspberry Pi itself to connect to its own console port (virtually), I tried this without luck:
screen /dev/ttyAMA0 115200 8N1.