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élanSC300 Microcontroller Data Sheet
59
P R E L I M I N A R Y
mode, as soon as VSYS is powered up, RSTDRV is im-
mediately driven High and will remain High until the
IORESET
signal is deasserted and the preserved pro-
grammed value in the PLL start-up timer has expired.
Force Term
Figure 4 on page 57 shows the schematic diagram,
and Table 24 shows the function of the IORESET,
RESIN, and Force Term. When in Micro Power Off
mode, it is important not to back power any of the pow-
ered-off internal power planes. Table 2
–Table 11 show
the VCCIO and VCC clamp voltage sources for each
signal pin. Ensure that all signals, which are either
driven by (VCCIO) or clamped to (VCC Clamp) a pow-
ered-off voltage source, are also either powered off or
driven Low.
PGP Pins
PGP2 and PGP3 can be programmed to be set to a
pre-defined state for Micro Power Off mode. For more
information, see the élan
TM
SC300 Microcontroller Pro-
grammer’s Reference Manual
, order # 18470.
Micro Power Off Mode Implementation
The system should not be powered up directly into
Micro Power Off mode. The system must be allowed to
fully power up into High Speed mode upon initial power
application of any power source. If a battery has insuf-
ficient power for the élanSC300 microcontroller to ini-
tialize into High Speed mode, the system design must
first power up the élanSC300 microcontroller from the
main source, and not allow the chip to be powered from
the battery until after it is fully initialized in High Speed
mode and properly transitioned into Micro Power Off
mode.
This requirement presents an issue when using (for ex-
ample) a 3-V Lithium battery cell as a back-up power
source to prevent the RTC from losing its contents dur-
ing Micro Power Off mode. If the battery is installed be-
fore any other power source is available, the
requirement cannot be met because such a small bat-
tery is incapable of supplying sufficient power to fully
initialize the system. The élanSC300 microcontroller
comes up in an undefined state, perhaps drawing suf-
ficient current to drain the battery.
The élanSC300 microcontroller backup power source
should be installed only after the system is powered by
the main power source prior to a transition into Micro
Power Off mode. When the system has transitioned
into Micro Power Off mode properly, the simultaneous
benefits of low power consumption while maintaining
RTC data such as time, date, and system configuration
can be realized.
Note:
The timing sequence and specifications for
power-up, entering, and exiting Micro Power Off mode
must be met. The timing specifications are shown in
Table 51 on page 99.
For more information, see the
élan
TM
SC300 and
élan
TM
SC310 Microcontrollers Solution For Systems
Using a Back-up Battery Application Note
, order
#20746 and the
Troubleshooting Guide for Micro
Power Off Mode on élan
TM
SC300 and élanSC310 Mi-
crocontrollers and Evaluation Boards Application Note
,
order #21810.
Table 24.
Internal I/O Pulldown States
IORESET
0
RESIN
0
Force Term
Active
Comments
This condition occurs when any power source is initially turned on. The
élanSC300 microcontroller’s core and analog VCC is transitioning to
on and RESIN is active (the initial power-up state). See the Micro Pow-
er Off Mode Implementation section below for more details.
This condition occurs when the core and analog VCC is stable, the
RESIN pin has been inactive, and the primary power supply outputs
are off (the normal Micro Power Off state).
This condition should be treated as condition 0,0 above.
This occurs when the secondary power supply is on, the RESIN
input is inactive, and the primary power supply is on and has deassert-
ed IORESET (normal system operating state).
0
1
Active
1
1
0
1
Active
Inactive