AN2434 Freescale Semiconductor / Motorola, AN2434 Datasheet - Page 3

• Manufacturer Part Number: AN2434
• Description: Input/Output (I/O) Pin Drivers
• Manufacturer: Freescale Semiconductor / Motorola

The simplified illustration of an output driver in
provide a current path between the output pin and both V
the p-channel FET is enabled. To drive the pin low, the n-channel FET is enabled. There is also a series
resistor in the output path. The effects of the FETs and the output resistance can be seen in the graphs
shown in
the current increases. The non-linear portion is due to the FET transfer function.
Pin Types
I/O pins are commonly grouped into 8-bit ports. In some cases there are fewer than eight bits available
on the pads for a given port. This generally is a result of pin-count limitations on the device package.
Smaller pin-count derivatives give up portions of several ports in order to fit in the smaller package, while
retaining as many of the higher-level peripheral functions as possible.
The I/O pins are further divided into those belonging to the processor core and those belonging to the port
integration module (PIM). The registers associated with the core and PIM ports are similar in function, but
different in layout. The pad drivers for these two port types are also different to accommodate the different
functions.
PIM Pins
The PIM is the portion of the MCU that supports the customized peripherals around the processor core.
Because the PIM provides the interface between the I/O pins and the non-standard peripherals on the
device, it provides a method to control all of the ports beyond ports A, B, E, and K.
Core Pins
Ports A and B are used for expanded mode address and data buses. Port E is used for control signals
(including ECLK and bus control). Port K is used for emulation chip select and expanded addressing. All
Freescale Semiconductor
Figure
11,
Figure
FROM INPUT
12,
Figure
Input/Output (I/O) Pin Drivers, Rev. 0
Figure 2. CMOS Output Stage
8, and
Figure
Figure 2
10. Notice the non-linear increase in voltage drop as
V
includes two FETs (field effect transistors) that
DD
Q1
Q2
DD
P-CHANNEL JFET
N-CHANNEL FET
and V
SS
PORT OUTPUT
(or ground). To drive the pin high,
Pin Types
3