UM10346_1
© NXP B.V. 2009. All rights reserved.
User manual
Rev. 01 — 2 November 2009
40 of 132
NXP Semiconductors
UM10346
LPC980/982 User manual
5.4 Regulators
Internal regulators can be adjusted automatically to minimize power consumption during
different power reduction modes. In normal or idle modes, power consumption can be
further reduced by configuring PMUCON register.
In normal or idle mode, regulators have two operation modes: high speed mode and low
current mode.
The regulators can be configured to low current mode to reduce the power consumption.
After power-on-reset, internal regulators enter high speed mode as default. PMUCON
register is used to configure the regulators’ operation modes. LPMOD bit is used to select
the regulators’ mode and HCOK bit is used to indicate whether the switch completed or
not. Before set LPMOD to select low current mode, please make sure the system
frequency no higher than 12 Mhz. When switch back to high speed mode, first clear
LPMOD bit to select high speed mode, then check HCOK bit. If HCOK bit turns to ‘1’, it
means the switch was completed.
6.
Reset
The P1.5/RST pin can function as either an active low reset input or as a digital input,
P1.5. The RPE (Reset Pin Enable) bit in UCFG1, when set to 1, enables the external reset
input function on P1.5. When cleared, P1.5 may be used as an input pin.
Remark:
During a power-on sequence, The RPE selection is overridden and this pin will
always functions as a reset input. An external circuit connected to this pin should not hold
this pin low during a Power-on sequence as this will keep the device in reset. After
power-on this input will function either as an external reset input or as a digital input as
defined by the RPE bit. Only a power-on reset will temporarily override the selection
defined by RPE bit. Other sources of reset will not override the RPE bit.
Note:
During a power cycle, V
DD
must fall below V
POR
(see P89LPC980/982
data sheet,
Static characteristics
) before power is reapplied, in order to ensure a power-on reset.
Reset can be triggered from the following sources:
•
External reset pin (during power-on or if user configured via UCFG1);
•
Power-on detect;
Table 26.
PMU Control register (PMUCON - address FAh) bit allocation
Bit
7
6
5
4
3
2
1
0
Symbol
LPMOD
-
-
-
-
-
-
HCOK
Reset
0
x
x
x
x
x
x
1
Table 27.
PMU control register (PMUCON - address FAh) bit description
Bit Symbol
Description
0
HCOK
Regulators mode flag. HCOK bit is set when the switch from low current mode to high speed mode is
completed. It is cleared when switching to low current mode. This bit can be reset only by POR reset.
1:6 -
Reserved
7
LPMOD
Low current mode control. When cleared, high speed mode is selected; when set, low current mode is
selected.