Reset Generation
6-6
Élan™SC520 Microcontroller User’s Manual
System reset is a subset of the power-on reset sequence described in “Initialization” on
page 6-9.The only real difference between the two is that, for power-on reset, power is
being applied to the part in addition to the reset, and the stabilization of power supplies to
deassertion of the reset is specified. The two terms are otherwise synonymous in this
document.
6.5.2
System Reset with SDRAM Retention
The ÉlanSC520 microcontroller is capable of performing a system reset in which the
contents of the SDRAM system are maintained.
This function, called
programmable reset, is enabled via the PRG_RST_ENB bit in the
Reset Configuration (RESCFG) register (MMCR offset D72h). If this bit is set, assertion of
the PRGRESET pin, SYS_RST bit, watchdog timer system reset event, or AMDebug
system reset event while PWRGOOD is asserted will result in a system reset in which the
SDRAM configuration (SDRAM type, number of banks, refresh rate, etc.) is maintained so
that the contents of SDRAM are preserved.
Although the CFG3–CFG0 and RSTLD7–RSTLD0 pins are not latched, all other aspects
of this type of reset are the same as a system reset.
The system reset request is arbitrated with the internal SDRAM controller to ensure that
all SDRAM banks are idle prior to assertion of the reset. In addition, this arbitration allows
the SDRAM controller to complete the current SDRAM cycle. Figure 6-2 shows the
sequence of events following a PRGRESET assertion with the PRG_RST_ENB bit enabled.
Note: If a system reset request is not acknowledged by the SDRAM controller when the
PRG_RST_ENB configuration bit is set, a normal system reset occurs. In this event, the
PRG_RST_ENB bit is cleared. Clearing of the PRG_RST_ENB bit indicates that the
contents of the SDRAM were not maintained.
Figure 6-2
PRGRESET Timing
Notes:
1. Reset assertion from PRGRESET assertion is approximately 32 CPU clocks. All SDRAM banks are idle.
2. The PRG_RST_ENB bit in the Reset Configuration (RESCFG) register must be enabled.
3. The signal “cpu reset” is an internal signal, shown here for reference only. It is not available as an external pin.
1
PRGRESET
cpu reset
GPRESET
RST
Содержание Elan SC520
Страница 1: ...lan SC520 Microcontroller User s Manual Order 22004A...
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Страница 28: ...Introduction xxviii lan SC520 Microcontroller User s Manual...
Страница 42: ...Architectural Overview 1 14 lan SC520 Microcontroller User s Manual...
Страница 78: ...System Initialization 3 22 lan SC520 Microcontroller User s Manual...
Страница 108: ...Clock Generation and Control 5 10 lan SC520 Microcontroller User s Manual...
Страница 118: ...Reset Generation 6 10 lan SC520 Microcontroller User s Manual...
Страница 148: ...System Arbitration 8 24 lan SC520 Microcontroller User s Manual...
Страница 214: ...SDRAM Controller 10 36 lan SC520 Microcontroller User s Manual...
Страница 230: ...Write Buffer and Read Buffer 11 16 lan SC520 Microcontroller User s Manual...
Страница 288: ...GP Bus DMA Controller 14 22 lan SC520 Microcontroller User s Manual...
Страница 316: ...Programmable Interval Timer 16 8 lan SC520 Microcontroller User s Manual...
Страница 328: ...Software Timer 18 4 lan SC520 Microcontroller User s Manual...
Страница 346: ...Real Time Clock 20 12 lan SC520 Microcontroller User s Manual...
Страница 360: ...UART Serial Ports 21 14 lan SC520 Microcontroller User s Manual...
Страница 414: ...AMDebug Technology 26 8 lan SC520 Microcontroller User s Manual...