MPC555CME Freescale Semiconductor, MPC555CME Datasheet - Page 89

• Manufacturer Part Number: MPC555CME
• Description: KIT EVALUATION FOR MPC555
• Manufacturer: Freescale Semiconductor
• Type: Microcontrollerr

Specifications of MPC555CME

• Contents: Module Board, Installation Guide, Power Supply, Cable, Software and more
• Processor To Be Evaluated: MPC555
• Data Bus Width: 32 bit
• Interface Type: RS-232
• For Use With/related Products: MPC555
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

2.4.6 Pull-Up and Pull-Down Enable and Disable for 3-V / 5-V Multiplexed Pins
2.4.6.1 PRDS Signal
2.4.6.2 Encoded 3-V / 5-V Select
2.4.6.3 Examples
MPC555
USER’S MANUAL
Two signals are needed to enable or disable the pull-up/pull-down devices in the 3-V
/ 5-V multiplexed pads:
The PRDS signal is derived from the PRDS bit in the PDMCR. A single signal controls
all affected pads (all pads related to SGPIO and all pads related to the UIMB modules).
The bit is reset by default (pull-ups enabled) and must be explicitly set by software af-
ter reset. The bit is reset immediately following power-on reset and by hard reset after
data coherency. This bit is not affected by soft reset.
This signal selects between the 3-V functionality and the 5-V functionality of the pin.
5-V operation is selected until the function of the pin is determined (based on the reset
configuration word) and PORESET is negated. At this point the 3-V / 5-V select signal
assumes the intended state (high for 5 V and low for 3 V).
Upon hard reset assertion, if the 3-V / 5-V select line is in 3-V select mode, it remains
in this mode until any external bus access completes. After this the 3-V / 5-V select
signal switches to 5-V mode to enable the pull-ups. This ensures that there is no con-
tention on the bus due to the pull-up being enabled. This signal is not affected by soft
reset.
Each pad group has a 3-V / 5-V select signal. Internal to the pad, logic combines these
signals to control the pull-up.
The combination of this 3-V / 5-V select signal and the resistor disable signal enables
or disables the pull-up.The logic to enable the pull-up is:
pull_enable = PRDS & 3-V / 5-V select
For example, if a pin is configured as a GPIO pin (5 V), the 3-V / 5-V select is high
throughout reset. This causes the pull-up to be enabled. At the end of reset, the 3-V /
5-V select line remains high. The PRDS is high by default until cleared by software.
This causes the pull-up to be enabled until software clears the PRDS bit in the PDM-
CR.
If a pin is configured as a bus pin (3 V), the 3 V / 5 V remains high throughout reset.
This causes the pull-up to be enabled. At the end of reset, the 3-V / 5-V select line goes
low. This causes the pull-up to be disabled, preventing any power loss if the MCU
starts fetching from external memory immediately out of reset.
• The PRDS signal
• An encoded 3-V / 5-V select
/
MPC556
SIGNAL DESCRIPTIONS
Rev. 15 October 2000
MOTOROLA
2-31