Real-Time Clock
Élan™SC520 Microcontroller User’s Manual
20-5
In this configuration, the RTC is reset after power-up, but is not reset by subsequent
PWRGOOD assertions.
■
The RTC is reset after a power-up—When power has been removed from the RTC, the
contents are no longer valid. In this case, the RTC is reset.
■
RTC is not reset—When a reset switch tied to PWRGOOD is pressed (V
CC
remains
High) and PWRGOOD reasserts with BBATSEN High, the RTC is not reset. In this case,
power did not go away, the RTC contents are still valid, and no RTC reset occurs.
Detailed component specifications for the resistor and capacitor shown in Figure 20-4 can
be found in the
Élan™SC520 Microcontroller Data Sheet, order #22003.
Figure 20-4
Circuit without Backup Battery
20.3.2
Selecting and Interfacing a 32.768-kHz Crystal
See the
Élan™SC520 Microcontroller Data Sheet, order #22003, for information and
detailed specifications for selecting a 32.768-kHz crystal.
20.3.3
Using an External RTC
When the ÉlanSC520 microcontroller comes out of reset, the internal RTC is enabled. If
the system application requires the use of an external RTC, the internal RTC should be
disabled during the boot process and initialization to prevent potential conflicts.
The Address Decode Control (ADDDECCTL) register (MMCR offset 80h) includes a control
bit for selecting between the internal RTC and an external RTC. Setting the RTC_DIS bit
to 1 disables the internal RTC by disabling the internal I/O decode for addresses 0070h
and 0071h. When the RTC_DIS bit is set, accesses to these addresses generate external
bus cycles, allowing the use of an external RTC module.
Disabling the internal RTC does not automatically disable the interrupt connection to the
programmable interrupt controller (PIC). If PC/AT-compatibility is required, the designer
should connect the external RTC’s interrupt request to one of the ÉlanSC520
VCC_ANLG
C1
R1
C2
Élan™SC520 Microcontroller
VCC_RTC
BBATSEN
Содержание Elan SC520
Страница 1: ...lan SC520 Microcontroller User s Manual Order 22004A...
Страница 4: ...iv lan SC520 Microcontroller User s Manual...
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...