Power-On Reset And Hard Reset; Pull-Up/Pull-Down; Pull-Up/Pull-Down Enable And Disable For 5-V Only And 2.6-V Only Signals; Pull-Down Enable And Disable For 5-V/2.6-V Multiplexed Signals - Motorola MPC533 Reference Manual

All signals are initialized to a "reset state" during reset. This state remains active until reset
is negated or until software disables the pull-up or pull-down device based on the signal
functionality. Upon assertion of the corresponding bits in the signal control registers and
negation of reset, the signal acquires the functionality that was programmed.
2.6.3

Power-On Reset and Hard Reset

Power-on reset and hard reset affect the functionality of the signals out of reset. (During
soft reset, the functionality of the signals is unaltered.)
Upon assertion of the power-on reset signal (PORESET/TRST) the functionality of the
signal is not yet known to the RCPU. The weak pull-up or weak pull-down resistors are
enabled. The reset configuration word configures the system, and towards the end of reset
the signal functionality is known. Based upon the signal functionality, the pull-up or
pull-down devices are either disabled immediately at the negation of reset or remain
enabled, as shown in Table 25-15.
Because hard reset can occur when a bus cycle is pending, the PDMCR bits that enable and
disable the pull-up or pull-down resistors are set or reset synchronously to eliminate
contention on the signals. (PORESET/TRST affects these bits asynchronously.)
2.6.4

Pull-Up/Pull-Down

2.6.4.1 Pull-Up/Pull-Down Enable and Disable for 5-V Only and 2.6-V
Only Signals
The pull resistors are enabled and disabled by the corresponding bits in the PDMCR
register in the USIU (see Table 25-15). When those bits are negated (logic 0), the pull
resistors are enabled. When asserted (logic 1), the devices are disabled.
2.6.4.2 Pull-Down Enable and Disable for 5-V/2.6-V Multiplexed
Signals
The 5-V/2.6-V multiplexed pad does not have a pull-up device. The pull-down will be
controlled by the corresponding bits in the PDMCR register. When this bit is negated, the
pull-down is enabled, when asserted the pull-down will be disabled.
All pull-up/pull-down devices are disabled when all the signals
are forced to three state in JTAG mode.
MOTOROLA
PRELIMINARY—SUBJECT TO CHANGE WITHOUT NOTICE
NOTE
Chapter 2. Signal Descriptions
Reset State
2-27