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106 CHAPTER THREE
Universal Serial Bus (USB)
USB is a serial standard (using a thin cable) that is
capable of transfers at around 1.5 MBps. It’s well known in the PC industry and
enables peripherals to be plugged in and out of the computer quickly, even with
the power turned on. For robots, a USB might be an easy way to hook into another
computer for communication or downloading. Many portable PCs support this
standard and could be brought up to the robot to service it. For more info, go to
www.quatech.com/Application_Objects/FAQs/comm-over-usb.htm.
Firewire, IEEE1394 The Firewire standard is generally used in systems requir-
ing a great deal of media data (audio or video). Cameras and other media devices
connect together using thin, hot-patch serial cables. Audio and video can be trans-
ferred in real time, without interruptions, between devices. One peculiarity of
media streams is that they cannot be interrupted without a noticeable degradation
of the transmission. If an interruption occurs in a digital video stream, for exam-
ple, blocks can be seen on the screen. The Firewire protocol is designed to guar-
antee the delivery of media data across the timeshared wire. If the robot must
transfer video or audio data, Firewire might be a good candidate for those trans-
missions. Broadcast video requires a transmission bandwidth of around 15 to 34
MBps. Firewire can handle around 50 MBps (to accommodate multiple trans-
mission streams) and faster versions are planned. For further info, go to
www.interfacebus.com/Design_Connector_Firewire.html.
Controller area network (CAN) The CAN bus is a serial bus standard designed
for use in electrically noisy environments such as automobiles and industrial sites.
It can transfer data at up to 125 KBps over cables from 40 to 1,000 meters long
(depending on data rates). Its other major advantage is that it saves wiring cost, an
important consideration when making thousands of automobiles. If the robot gen-
erates a great deal of electrical noise from its motors, then CAN might be a good
choice for the electrical bus inside the robot (www.interfacebus.com/Design_
Connector_CAN.html).
Inter-IC (I2C) I2C is a serial bus standard used largely for signaling within a
single PCB, although at least one version of the protocol uses a cable. Its primary
value is to save pin count on small chips that require slow, complex data trans-
missions. If the robot is short on PCB real estate, then I2C chips can save quite a
bit of room. The maximum bandwidth is around 400 KBps (www.interfacebus
.com/Design_Connector_I2C.html).

Network
No discussion of I/O would be complete without a discussion of LAN I/O. Almost every
computer system has a network interface, whether it’s hooked up or not. In everyday