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2-16 Intel® PXA255 Processor Developer’s Manual
System Architecture
48MHz/GP[7] ICOCZ
48 MHz clock. (output) Peripheral clock output derived
from the PLL.
NOTE: This clock is only generated when the USB unit
clock enable is set.
Pulled High -
Note[1]
Note [3]
RTCCLK/
GP[10]
ICOCZ
Real time clock. (output) 1 Hz output derived from the
32kHz or 3.6864MHz output.
Pulled High -
Note[1]
Note [3]
3.6MHz/GP[11] ICOCZ
3.6864 MHz clock. (output) Output from 3.6864 MHz
oscillator.
Pulled High -
Note[1]
Note [3]
32kHz/GP[12] ICOCZ 32 kHz clock. (output) Output from the 32 kHz oscillator.
Pulled High -
Note[1]
Note [3]
Miscellaneous Pins
BOOT_SEL
[2:0]
IC Boot select pins. (input) Indicates type of boot device. Input Input
PWR_EN OC
Power Enable for the power supply. (output) When
negated, it signals the power supply to remove power to
the core because the system is entering sleep mode.
Driven High
Driven low while
entering sleep
mode. Driven high
when sleep exit
sequence begins.
nBATT_FAULT IC
Main Battery Fault. (input) Signals that main battery is
low or removed. Assertion causes PXA255 processor to
enter sleep mode or force an Imprecise Data Exception,
which cannot be masked. PXA255 processor will not
recognize a walk-up event while this signal is asserted.
Minimum assertion time for nBATT_FAULT is 1 ms.
Input Input
nVDD_FAULT IC
VDD Fault. (input) Signals that the main power source is
going out of regulation. nVDD_FAULT causes the
PXA255 processor to enter sleep mode or force an
Imprecise Data Exception, which cannot be masked.
nVDD_FAULT is ignored after a walk-up event until the
power supply timer completes (approximately 10 ms).
Minimum assertion time for nVDD_FAULT is 1 ms.
Input Input
nRESET IC
Hard reset. (input) Level sensitive input used to start the
processor from a known address. Assertion causes the
current instruction to terminate abnormally and causes a
reset. When nRESET is driven high, the processor starts
execution from address 0. nRESET must remain low until
the power supply is stable and the internal 3.6864 MHz
oscillator has stabilized.
Input
Input. Driving low
during sleep will
cause normal
reset sequence
and exit from sleep
mode.
nRESET_OUT OC
Reset Out. (output) Asserted when nRESET is asserted
and deasserts after nRESET is deasserted but before the
first instruction fetch. nRESET_OUT is also asserted for
“soft” reset events: sleep, watchdog reset, or GPIO reset.
Driven low during
any reset sequence
- driven high prior to
first fetch.
Driven Low
JTAG and Test Pins
nTRST IC
JTAG Test Interface Reset. Resets the JTAG/Debug
port. If JTAG/Debug is used, drive nTRST from low to
high either before or at the same time as nRESET. If
JTAG is not used, nTRST must be either tied to nRESET
or tied low.
Input Input
TDI IC
JTAG test data input. (input) Data from the JTAG
controller is sent to the PXA255 processor using this pin.
This pin has an internal pull-up resistor.
Input Input
Table 2-6. Pin & Signal Descriptions for the PXA255 Processor (Sheet 8 of 9)
Pin Name Type Signal Descriptions Reset State Sleep State