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P5040/P5020 Reference Design Board User Guide, Rev. 0
44
Freescale Semiconductor
Configuration
5.5.3
Reset controller considerations
When creating the reset controller, consider the following:
PWRGD
Functions as general system reset (from ATX power supply).
COP_TRST
Assert during normal, non-COP startup.
COP_HRST
If asserted by COP then do not assert COP_TRST.
Resets the target system and processor HRESET inputs.
HRESET_REQ
Only has two-three clock cycles and requires pulse stretching.
SHMOO/Test Tracking
Register PX_AUX must be reset by all reset sources except COP_HRST and
WDOG_RST.
6
Configuration
This figure shows the configuration logic for signals configured using DIP-switches.
Figure 20. Configuration Logic
Configuration logic has several options, as follows:
•
ngPIXIS, by default, transfers switch settings to the processor configuration pin during the
HRESET_B assertion interval.
•
Software running on the P5040/P5020 can initialize internal registers (SWx, ENx) that allow a
board to configure itself for the next restart; this is called self-SHMOO or self-characterization.
•
At reset, ngPIXIS copies configuration data from an external I
2
C EEPROM and applies these
values to the SWx/ENx registers (while ignoring external hardware switches).
6.1
Configuration Options
There are three configuration options, as follows:
1. Require software configuration in order to support evaluation.
2. Easily and frequently changed by the end-user/developer.
P5040/P3041/P5020
CONFIG_PIN
ngPIXIS
where needed
OVDD
CFGDRV
SW1
EN1
SW2
EN2
...
ngPIXIS
EEPROM
ENx.y
SWx.y