Hardware Reference
In-Depth Information
1. Three timers (two 8-bit timers and one 16-bit timer).
2. Real-time clock with oscillator.
3. Six pulse-width modulation channels used, for example, to control
light intensity or motor speed.
4. Eight analog-to-digital conversion channels used to read voltage lev-
els.
5. Universal serial receiver/transmitter.
6. I2C serial interface, a common standard for interfacing to sensors.
7. Programmable watchdog timer that detects when the system has
locked up.
8. On-chip analog comparator that compares two input voltages.
9. Power brown-out detector that interrupts the system when power is
failing.
10.
Internal programmable clock oscillator to drive the CPU clock.
To avoid any confusion, it is worth stating explicitly that in this topic, as in
computer science in general, metric units are used instead of traditional English
units (the furlong-stone-fortnight system). The principal metric prefixes are listed
in Fig. 1-16. The prefixes are typically abbreviated by their first letters, with the
units greater than 1 capitalized (KB, MB, etc.). One exception (for historical rea-
sons) is kbps for kilobits/sec. Thus, a 1-Mbps communication line transmits 10
6
bits/sec and a 100-psec (or 100-ps) clock ticks every 10
−10
seconds. Since milli
and micro both begin with the letter ''m,'' a choice had to be made. Normally,
''m'' is for milli and ''
μ
'' (the Greek letter mu) is for micro.
It is also worth pointing out that in common industry practice for measuring
memory, disk, file, and database sizes, the units have slightly different meanings.
There, kilo means 2
10
(1024) rather than 10
3
(1000) because memories are always
a power of two. Thus, a 1-KB memory contains 1024 bytes, not 1000 bytes. Simi-
larly, a 1-MB memory contains 2
20
(1,048,576) bytes, a 1-GB memory contains 2
30
(1,073,741,824) bytes, and a 1-TB database contains 2
40
(1,099,511,627,776)
bytes.
However, a 1-kbps communication line can transmit 1000 bits per second and
a 10-Mbps LAN runs at 10,000,000 bits/sec because these speeds are not powers
of two. Unfortunately, many people tend to mix up these two systems, especially
for disk sizes.
