Hardware Reference
In-Depth Information
to the Core i7 rabbit, but the turtle uses much less power, and the turtle may finish
first, especially if the rabbit's battery is not very big.
Both the Core i7 and the OMAP4430 are examples of high-performance com-
puting platforms designed for building highly capable computing devices, with the
Core i7 focusing on desktop applications while the OMAP4430 focuses on mobile
applications. When many people think about computers, systems like these come
to mind. However, another whole world of computers exists that is actually far
more pervasive: embedded systems. In this section we will take a brief look at that
world.
It is probably only a slight exaggeration to say that every electrical device cost-
ing more than $100 has a computer in it. Certainly televisions, cell phones, elec-
tronic personal organizers, microwave ovens, camcorders, VCRs, laser printers,
burglar alarms, hearing aids, electronic games, and other devices too numerous to
mention are all computer controlled these days. The computers inside these things
tend to be optimized for low price rather than for high performance, which leads to
different trade-offs than the high-end CPUs we have been studying so far.
PC6
PD0
PD1
PD2
PD3
PD4
VCC
GND
PB6
PB7
PD5
PD6
PD7
PB0
PC5
PC4
PC3
PC2
PC1
PC0
GND
AREF
AVCC
1
2
3
4
5
6
7
8
9
10
11
12
13
14
28
27
26
25
24
23
22
21
20
19
18
17
16
15
PB5
PB4
PB3
PB2
PB1
Figure 3-49.
Physical pinout of the ATmega168.
As we mentioned in Chap. 1, the Atmel ATmega168 microcontroller is widely
used, mostly due to its very low cost (about $1). As we will see shortly, it is also a
versatile chip, which makes interfacing to it simple and inexpensive. So let us now
examine this chip, whose physical pinout is shown in Fig. 3-49.
As can be seen from the figure, the ATmega168 normally comes in a standard
28-pin package (although other packages are available). At first glance, you proba-
bly noticed that the pinout on this chip is a bit strange compared to the previous
two designs we examined. In particular, this chip has no address and data lines.
This is because the chip is not designed to be connected to memory, only to de-
vices. All of the memory, SRAM and flash, is contained within the processor, obvi-
ating the need for any address and data pins as shown in Fig. 3-50.
