Hardware Reference
In-Depth Information
connect the red wire to the 5 V pin (P1-04), then without any other power
source connected, plug the USB-to-TTL Serial cable into your laptop. The
Raspberry Pi will boot up!
This is really just a parlor trick, because the power coming off that red wire
is not the ideal way to power the Raspberry Pi for a number of reasons, as
discussed in
“Think Twice Before Using the GPIO to Power the Pi” on page
25
.
Figure 1-10.
A properly wired USB to TTL serial cable
Now, go ahead and connect the USB connector to your computer.
To connect to the UART serial device, you first need to know its device name. The
kernel assigns it a device name when the USB serial driver successfully loads (which
it should have already done when you inserted the USB end of the cable), so you just
need to look through the output from dmesg.
Specifically, we know that the device name will be
ttyUSB#
, where
#
is a number. It's
probably
ttyUSB0
, but let's look to be sure. If you have multiple USB serial devices
present on your system (you naughty super hacker, you), you're looking for the one
with the pl2303 converter type. If you have more than one pl2303 converter type USB
serial device present, pick one at a time and try until you find the right one. Anyway,
here's how you can check:
$ dmesg | grep -B2 ttyUSB
[23882.896558] usbserial: USB Serial support registered for pl2303
[23882.896578] pl2303 1-1.5.1:1.0: pl2303 converter detected
[23882.898285] usb 1-1.5.1: pl2303 converter now attached to ttyUSB0
Sure enough, our device is
ttyUSB0
. This means that the full device node name is
/dev/
ttyUSB0
. Unprivileged users do not normally have access to
/dev/ttyUSB#
devices; you
need to be in a special group. If you look at the file permissions on the device node
