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P80C31BH-1 View Datasheet(PDF) - Intel

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P80C31BH-1 Datasheet PDF : 21 Pages
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87C51 80C51BH 80C31BH
IDLE MODE
In Idle Mode the CPU puts itself to sleep while all
the on-chip peripherals remain active The mode is
invoked by software The content of the on-chip
RAM and all the Special Functions Registers remain
unchanged during this mode The Idle Mode can be
terminated by any enabled interrupt or by a hard-
ware reset
It should be noted that when Idle is terminated by a
hardware reset the device normally resumes pro-
gram execution from where it left off up to two ma-
chine cycles before the internal reset algorithm
takes control On-chip hardware inhibits access to
internal RAM in this event but access to the port
pins is not inhibited To eliminate the possibility of an
unexpected write to a port pin when Idle is terminat-
ed by reset the instruction following the one that
invokes Idle should not be one that writes to a port
pin or to external memory
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 transmitted
On the 87C51 BH either a hardware reset or an ex-
ternal interrupt can cause an exit from Power Down
Reset redefines all the SFR’s but does not change
the on-chip RAM An external interrupt allows both
the SFRs and on-chip RAM to retain their values
To properly terminate Power Down the reset or ex-
ternal interrupt should not be executed before VCC is
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 and INT1 must be
enabled 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
RET1 will be the one following the instruction that
put the device into Power Down
DESIGN CONSIDERATIONS
 Exposure to light when the device is in operation
may cause logic errors For this reason it is sug-
gested that an opaque label be placed over the
window when the die is exposed to ambient light
 The 87C51 BH now have some additional fea-
tures The features are asynchronous port reset
4 interrupt priority levels power off flag ALE dis-
able serial port automatic address recognition
serial port framing error detection 64-byte en-
cryption array and 3 program lock bits These
features cannot be used with the older versions
of 80C51BH 80C31BH The newer version of
80C51BH 80C31BH will have change identifier
‘‘A’’ appended to the lot number
Mode
Idle
Idle
Power Down
Power Down
Table 2 Status of the External Pins during Idle and Power Down
Program
Memory
ALE
PSEN
PORT0
PORT1
PORT2
Internal
1
1
Data
Data
Data
External
1
1
Float
Data
Address
Internal
0
0
Data
Data
Data
External
0
0
Float
Data
Data
PORT3
Data
Data
Data
Data
6
 

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