8XL525458

POWER DOWN MODE

To save even more power a Power Down mode can

be invoked by software In this mode the oscillator

is stopped and the instruction that invoked Power

Down is the last instruction executed The on-chip

RAM and Special Function Registers retain their val-

ues until the Power Down mode is terminated

On the 8XL5X either hardware reset or external in-

terrupt can cause an exit from Power Down Reset

redefines all the SFRs but does not change the on-

chip RAM An external interrupt allows both the

SFRs and the on-chip RAM to retain their values

To properly terminate Power Down the reset or ex-

restored to its normal operating level and must be

held active long enough for the oscillator to restart

and stabilize (normally less than 10 ms)

With an external interrupt INT0 or INT1 must be en-

abled and configured as level-sensitive Holding the

pin low restarts the oscillator but bringing the pin

back high completes the exit Once the interrupt is

serviced the next instruction to be executed after

RETI will be the one following the instruction that put

the device into Power Down

DESIGN CONSIDERATION

frequency range of 35 MHz to 16 MHz (Ex-

press)20 MHz (Commercial) Operating beyond

these specifications could cause improper device

functionality

refer to Figure 2 Pin Connections for the specific

pins

reset the device normally resumes program exe-

cution from where it left off up to two machine

cycles before the internal reset algorithm takes

control On-chip hardware inhibits access to inter-

nal RAM in this event but access to the port pins

is not inhibited To eliminate the possibility of an

unexpected write when Idle is terminated by re-

set the instruction following the one that invokes

Idle should not be one that writes to a port pin or

to external memory

ONCE MODE

The ONCE (‘‘On-Circuit Emulation’’) Mode facilitates

testing and debugging of systems using the 8XL5X

without the 8XL5X having to be removed from the

circuit The ONCE Mode is invoked by

1) Pull ALE low while the device is in reset and

PSEN is high

2) Hold ALE low as RST is deactivated

While the device is in ONCE Mode the Port 0 pins

float and the other port pins and ALE and PSEN are

weakly pulled high The oscillator circuit remains ac-

tive While the 8XL5X is in this mode an emulator or

test CPU can be used to drive the circuit Normal

operation is restored when a normal reset is applied

Table 1 Status of the External Pins during Idle and Power Down

Mode

Program

ALE

PSEN

PORT0

PORT1

PORT2

PORT3

Memory

Idle

Internal

1

1

Data

Data

Data

Data

Idle

External

1

1

Float

Data

Address

Data

Power Down

Internal

0

0

Data

Data

Data

Data

Power Down

External

0

0

Float

Data

Data

Data

NOTE

For more detailed information on the reduced power modes refer to current Embedded Microcontrollers and Processors

Handbook Volume I

270646 and Application Note AP-252 (Embedded Applications Handbook)

270648 ‘‘Designing

with the 80C51BH’’

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