Hardware Reference
In-Depth Information
PU0/M0C0P
PU1/M0C0M
PV0/M2C0P
PV1/M2C0M
PW0/M4C0P
PW1/M4C0M
PU2/M0C1P
PV2/M2C1P
PW2/M4C1P
PU3/M0C1M
PV3/M2C1M
PW3/M4C1M
PU4/M1C0P
PV4/M3C0P
PW4/M5C0P
PU5/M1C0M
PV5/M3C0M
PW5/M5C0M
PU6/M1C1P
PV6/M3C1P
PW6/M5C1P
PU7/M1C1M
PV7/M3C1M
PW7/M6C1M
(b) Port V
(a) Port U
(c) Port W
Figure 7.23
■
Port U, V, and W pins and their alternate functions
The functions of these port pins are shown in Figure 7.23a-c, respectively.
Most embedded systems require the use of logic chips, peripheral devices in addition to
the microcontroller, to perform their function. Because these chips may use different types of
integrated circuit (IC) technologies, there is a concern that the resultant embedded system may
not function properly.
The major concern in interfacing IC chips that are made with different technolo-
gies is whether they are electrically compatible. There are two issues involved in electrical
compatibility.
•
Voltage-level compatibility
. Is the high output level of an IC chip high enough to
be considered as a high for the input of another IC chip? Is the low output level of
an IC chip low enough to be considered as a low for the input of another IC chip?
•
Current drive capability
. Does the output of an IC chip have enough current to
drive its load? Can the output circuit of an IC chip sink the currents of its load?
Signal timing is also an important factor for making sure that the digital circuit functions cor-
rectly. The main concern about timing is whether the signal from one chip becomes valid early
enough to be used by other chips. This is a
timing compatibility
issue. When the operating fre-
quency becomes very high, the
transmission line effect
and
ground bounce effect
will need to
be considered too. However, we are not dealing with high-frequency systems in this text. These
two issues will not be discussed.
There are many IC technologies in use today. Some of them are bipolar; others are uni-
polar. A bipolar IC technology has both the electron and hole currents in any moment. How-
ever, in a unipolar IC technology, the current in any part of the circuit is either the electron
current or the hole current. The unipolar CMOS technology is the dominant IC technology
in use today.
Search WWH ::
Custom Search