AN2434 Freescale Semiconductor / Motorola, AN2434 Datasheet - Page 10

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

Source and Sink for Full-Drive Currents
current are shown in
(GPIO) pin is shown. The GPIO pins are contained in two sections of the MCU:
The core includes ports A, B, E, and K. The port integration module (PIM) includes ports M, P, S, T, H,
and J. Data was collected for ports A0, A7, B7, E7, and K5. Plotted data for port A0 is representative of
all the port pins based on previous testing.
The graphs also show a dashed vertical line to indicate the maximum current for which the pad drivers
were designed. The current and voltage thresholds specified in the device electrical specification are
shown for comparison.
The electrical specification section of the device user guide specifies the absolute maximum amount of
current source or sink. For example, the 9S12DP256 user guide specifies that the maximum amount of
current source or sink allowed for any single I/O pin is ±25 mA.
currents can be supplied, however V
result. The factory specifications are conservative to ensure that all devices meet the specifications while
taking into account normal voltage, temperature, and process variation. Sourcing or sinking more current
than the absolute maximum ratings can damage the MCU.
When this document was written, the MC9S12 Family did not specify maximum current for all pins
combined. (Limits are implied by device thermal characteristics, which are described in the device user
guide or data sheet.) Some other MCUs have both a maximum pin current specified (before V
may go out of specification) and a maximum total device current specified (to prevent metal migration).
Source and Sink for Full-Drive Currents
To test the current that an output pin can source, the output pin is tied via a resistor to ground (V
Figure
constant and the current flowing out of the pin is measured. For this series of tests, the voltage and current
are measured with two digital multimeters. The values are recorded and plotted in the following sections.
Voltage (the independent variable) is plotted on the Y axis, and current (the dependent variable) is plotted
on the X axis in
10
•
•
Core
Port integration module (PIM)
7). The resistance is then varied while the voltage (with respect to ground) is held (relatively)
Figure 8
Figure 8
and
Figure
and
Figure
OH
PORT A0
Input/Output (I/O) Pin Drivers, Rev. 0
11.
and V
Figure 7. Source Circuit
11. To simplify the graph, one general-purpose input/output
V
OL
OH
V
specifications do not apply and damage to the MCU may
I
Source
R
Figure 8
and
Figure 10
Freescale Semiconductor
show that higher
OL
and V
SS
) (see
OH