MPC555
/
MPC556
SIGNAL DESCRIPTIONS
MOTOROLA
USER’S MANUAL
Rev. 15 October 2000
2-37
2.5 Pad Types
There are different pad types based on functional characteristics. Even pads with the
same functionality may be different due to different electrical characteristics. All 5-V
inputs have hysteresis. There is no synchronization in the pads; it is all in the modules.
2.5.1 Pad Interface Signals
The pad interface consists of an internal interface and an external interface. The ex-
ternal interface is to the pin. The internal interface is the set of signals that interface
the pad to the chip’s internal logic. The following internal interface signals are used:
• Data – The line driven from an internal module of the chip to the pad. For bi-di-
rectional pins, the internal interface may be a single line for both input and output
or two separate paths for input and output. The descriptions of individual pad
types specify which.
• 3-V / 5-V select – Selects a 3-V or 5-V driver, for pads that support both. This sig-
nal is driven from the USIU.
• Output enable (OE) – Enables the output driver. For 3-V / 5-V pads, the appropri-
ate driver is enabled based on the pin functionality selected.
• Input enable – Enables the receiver. For 3-V / 5-V pads, the appropriate receiver
is enabled based on the pin functionality selected.
CMF
EPEE
EPEE
I
3 V
PD
VPP
VPP
I
5 V
—
VDDF
VDDF
I
3 V
—
VSSF
VSSF
I
3 V
—
Global Power Supplies
VDDL
VDDL
I
3 V
—
VDDH
VDDH
I
5 V
—
VDDI
VDDSI
I
3 V
—
VSSI
VSSI
I
3 V
—
KAPWR
3
KAPWR
I
3 V
—
VDDSRAM
VDDSRAM
I
3 V
—
VDDSYN
VDDSYN
I
3 V
—
VSS
VSS
I
—
—
VSSSYN
VSSSYN
I
3 V
—
NOTES:
1. During reset, the output enable to the pad driver is negated and the PU3/PU5 is active. After reset is negated,
the output enable is continuously enabled and the PU3 is disabled. The driver is responsible for driving a
valid state on the pin.
2. Pull-up/pull-down is active when pin is defined as an input and/or during reset; therefore, output enable is
negated. This also means that external pull-up/pull-down is
not
required unless specified.
3. These pins are powered by KAPWR (Keep-Alive Power Supply).
4. This pin is an active negate signal and may need an external pull-up resister.
Table 2-4 Pin Reset State (Continued)
Pin
Function
Port
Voltage
Reset State
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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