AT89C51ED2-RDTUM datasheet(82/137 Pages) ATMEL

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4235K–8051–05/08

AT89C51RD2/ED2

continue for a number of clock cycles before the internal reset algorithm takes

control. Reset initializes the AT89C51RD2/ED2 and vectors the CPU to address

0000h.

Generate an enabled external Keyboard interrupt (same behavior as external interrupt).

Note:

During the time that execution resumes, the internal RAM cannot be accessed; however, it is pos-

sible for the Port pins to be accessed. To avoid unexpected outputs at the Port pins, the instruction

immediately following the instruction that activated the Power-Down mode should not write to a

Port pin or to the external RAM.

Note:

Exit from power-down by reset redefines all the SFRs, but does not affect the internal RAM

content.

Table 18-1.

Pin Conditions in Special Operating Modes

Mode

Port 0

Port 1

Port 2

Port 3

Port 4

ALE

PSEN#

Reset

Floating

High

Idle (internal

code)

Data

High

Idle (external

code)

Floating

Data

High

Power-Down

(internal

code)

Data

Low

Power-Down

(external

code)

Floating

Data

Low

AT89C51ED2-RDTUM Datasheet(PDF) 82 Page - ATMEL Corporation

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