© Koninklijke Philips Electronics N.V. 2005. All rights reserved.
User manual
Rev. 03 — 7 June 2005
111 of 139
Philips Semiconductors
UM10119
P89LPC938 User manual
16.5 Power-down operation
The WDT oscillator will continue to run in power-down, consuming approximately 50
µ
A,
as long as the WDT oscillator is selected as the clock source for the WDT. Selecting PCLK
as the WDT source will result in the WDT oscillator going into power-down with the rest of
the device (see
). Power-down mode will also prevent PCLK from running and
therefore the watchdog is effectively disabled.
16.6 Periodic wake-up from power-down without an external oscillator
Without using an external oscillator source, the power consumption required in order to
have a periodic wake-up is determined by the power consumption of the internal oscillator
source used to produce the wake-up. The Real-time clock running from the internal RC
oscillator can be used. The power consumption of this oscillator is approximately 300
µ
A.
Instead, if the WDT is used to generate interrupts the current is reduced to approximately
50
µ
A. Whenever the WDT underflows, the device will wake-up.
17. Additional features
The AUXR1 register contains several special purpose control bits that relate to several
chip features. AUXR1 is described in
Table 105: AUXR1 register (address A2h) bit allocation
Bit
7
6
5
4
3
2
1
0
Symbol
CLKLP
EBRR
ENT1
ENT0
SRST
0
-
DPS
Reset
0
0
0
0
0
0
x
0
Table 106: AUXR1 register (address A2h) bit description
Bit Symbol
Description
0
DPS
Data Pointer Select. Chooses one of two Data Pointers.
1
-
Not used. Allowable to set to a logic 1.
2
0
This bit contains a hard-wired 0. Allows toggling of the DPS bit by incrementing
AUXR1, without interfering with other bits in the register.
3
SRST
Software Reset. When set by software, resets the P89LPC938 as if a hardware
reset occurred.
4
ENT0
When set the P1.2 pin is toggled whenever Timer 0 overflows. The output
frequency is therefore one half of the Timer 0 overflow rate. Refer to
for details.
5
ENT1
When set, the P0.7 pin is toggled whenever Timer 1 overflows. The output
frequency is therefore one half of the Timer 1 overflow rate. Refer to
for details.
6
EBRR
UART Break Detect Reset Enable. If logic 1, UART Break Detect will cause a chip
reset and force the device into ISP mode.
7
CLKLP
Clock Low Power Select. When set, reduces power consumption in the clock
circuits. Can be used when the clock frequency is 8 MHz or less. After reset this bit
is cleared to support up to 12 MHz operation.
