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Reset Generation Registers
3-6
élanSC520 Microcontroller Register Set Manual
Programming Notes
Unlike most other registers, the bits in this register are only returned to their reset value by a PWRGOOD reset. They
are not cleared by any other kind of reset.
The AMDebug technology trace information is preserved only if a soft reset is generated to the CPU.
See the
élanSC520 Microcontroller User’s Manual
, order #22004, for details about reset generation. Table 3-3
provides a summary of élanSC520 microcontroller reset sources and effects.
2
SD_RST_DET
CPU Shutdown Reset Detect
This bit is set when a CPU shutdown cycle (typically caused by a software “triple-fault”) is
detected. Software clears this bit by writing a 1.
0 =No CPU shutdown cycle was detected.
1 =The CPU soft reset event was from a shutdown cycle.
A soft reset event clears the NMI_ENB bit in the PICICR register (see page 12-4). This allows
software to initialize the stack pointer before setting the NMI_ENB bit again after a soft reset.
1
PRGRST_DET
PRGRESET Detect
This bit is set when a reset from PRGRESET pin is detected. Software clears this bit by
writing a 1.
0 =No PRGRESET pin reset was detected.
1 =The system reset event was from the PRGRESET pin.
If the PRG_RST_ENB bit is 1 in the RESCFG register (see page 3-3), assertion of the
PRGRESET pin while PWRGOOD is asserted results in a programmable reset in which the
SDRAM configuration is maintained.
0
PWRGOOD_
DET
POWERGOOD Reset Detect
This bit is set when a reset from the PWRGOOD pin is detected. Software clears this bit by
writing a 1.
0 =No PWRGOOD pin reset was detected.
1 =The system reset event was from the PWRGOOD pin.
This reset event has higher priority over PRGRESET and disables the PRGRESET function (if
it is enabled) by clearing the PRG_RST_ENB bit in the RESCFG register (see page 3-3).
Table 3-3
Microcontroller Reset Sources
Source
PWRGOOD pin
PRGRESET pin
CPU
(Hard/Soft)
Hard
Hard
GPRESET
Pin
RST Pin
(PCI)
Internal
Registers
Notes
1,2
Notes:
1. The PRG_RST_ENB bit must be set in the RESCFG register (see page 3-3) to enable the reset function on this pin.
2. If the PRG_RST_ENB bit is set, the SDRAM controller configuration is maintained to support system reset in which SDRAM
contents are also maintained.
3. Any write of a 1 to the CPU_RST bit causes a soft reset, regardless of whether the bit was previously 1 or 0.
SYS_RST bit, RESCFG register (see page 3-4)
Hard
2
Watchdog timer reset event (page 16-2)
Hard
2
AMDebug technology system reset
Hard
2
CPU_RST bit, SYSCTLA register (page 3-9)
Soft
3
SCP soft reset, SCPCMD register (page 3-7)
CPU shutdown (typically caused by a triple-fault)
GP_RST bit, RESCFG register (page 3-3)
PCI_RST bit, HBCTL register (page 6-3)
Soft
Soft
Bit
Name
Function