Datasheet

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7764A–8051–11/07
1.4 Microcontroller status
During hardware or firmware debugging, it is sometimes interesting to know what the state of the
microcontroller is. See table below for details.
Note: Port 0 can force a 0 level. A "one" will leave port floating.
Hardware
conditions Microcontroller status
RST EA ALE PSEN XTAL2 Mode P0 P1 P2 P3
Active 1 1 1 Flat Reset FF FF FF
Not active 1 Toggling 1 Toggling
Operating mode
Fetches internal code
Not active 1 1 1 Toggling
Idle mode
Does not fetch code
Port Data
(1)
Port Data Port Data Port Data
Not active 1 0 0 Flat
Power down mode
Does not fetch code
Port Data
(1)
Port Data Port Data Port Data
Active 0 1 1 Flat Reset FF FF FF FF
Not active 0 Toggling 1 Toggling
Operating mode
Fetches external code
Not active 0 1 1 Toggling
Idle mode
Does not fetch code
Floating Port Data Address Port Data
Not active 0 0 0 Flat
Power down mode
Does not fetch code
Floating Port Data Port Data Port Data