Hardware Reference
In-Depth Information
The two chip select pins mean you can control two SPI devices.
For those who would like to better understand GPIO and to effectively use this feature
of the Raspberry Pi, we recommend looking through
this page
, which provides an
access library for the Pi's GPIO. It will be particularly useful if you are already familiar
with Arduino wiring.
Add a USB Serial Console
HACK 16
Arguably the most common way to access embedded devices like the
Raspberry Pi is via the built-in serial device. This easy hack gives you a
USB serial console from your Raspberry Pi.
Almost all of the common embedded computers and microcontrollers available today
have built-in Universally Asynchrononous Receiver/Transmitters (UARTs). The UART
provides a mechanism for receiving and transmitting serial data, one bit at a time.
This method of serial communication is sometimes referred to as transistor-transistor
logic (TTL) serial. The data rate varies by device, but it is measured in bits per second.
The Raspberry Pi has a built-in UART connected to BCM Pins 14 (TXD) and 15 (RXD),
with a data rate of 115200bps (or baud).
Hey, That's Not Really Baud!
OK, from a semantic point of view, yes, baud is the unit of symbol rate, which
is not always identical to gross bit rate (bps). Wikipedia says that baud is
“the number of distinct symbol changes (signaling events) made to the
transmission medium per second in a digitally modulated signal or a line
code.” Then it goes on for several more pages of mathematical distinction
about baud, which may be fascinating to you or may put you to sleep.
The key takeaway is this: the computer and electronics industry has been
widely misusing the term baud for about 40 years now. As a result, lots of
software and hardware uses bps and baud interchangeably. In the specific
case of the USB serial console on the Raspberry Pi, the data rate in bps and
the baud rate are the same. The units here don't matter to us as much as
making sure you have a functional serial console, and for that, you need to
know that the data rate is 115200. Bits, baud, giant hamsters of doom, pick
your units as you will, but 115200 is the magic number for the Raspberry Pi
UART serial device.
