AT89C52_00 Datasheet, PDF (4/24 Pages) ATMEL Corporation – 8-bit Microcontroller with 8K Bytes Flash

timing or clocking purposes. Note, however, that one ALE
pulse is skipped during each access to external data
memory.
If desired, ALE operation can be disabled by setting bit 0 of
SFR location 8EH. With the bit set, ALE is active only dur-
ing a MOVX or MOVC instruction. Otherwise, the pin is
weakly pulled high. Setting the ALE-disable bit has no
effect if the microcontroller is in external execution mode.
PSEN
Program Store Enable is the read strobe to external pro-
gram memory.
When the AT89C52 is executing code from external pro-
gram memory, PSEN is activated twice each machine
cycle, except that two PSEN activations are skipped during
each access to external data memory.
Table 1. AT89C52 SFR Map and Reset Values
EA/VPP
External Access Enable. EA must be strapped to GND in
order to enable the device to fetch code from external pro-
gram memory locations starting at 0000H up to FFFFH.
Note, however, that if lock bit 1 is programmed, EA will be
internally latched on reset.
EA should be strapped to V_CC for internal program
executions.
This pin also receives the 12-volt programming enable volt-
age (V_PP) during Flash programming when 12-volt
programming is selected.
XTAL1
Input to the inverting oscillator amplifier and input to the
internal clock operating circuit.
XTAL2
Output from the inverting oscillator amplifier.
0F8H
0FFH
0F0H
B
00000000
0F7H
0E8H
0EFH
0E0H
ACC
00000000
0E7H
0D8H
0DFH
0D0H
0C8H
PSW
00000000
T2CON
00000000
T2MOD
XXXXXX00
RCAP2L
00000000
RCAP2H
00000000
TL2
00000000
TH2
00000000
0D7H
0CFH
0C0H
0C7H
0B8H
0B0H
0A8H
0A0H
98H
90H
88H
80H
4
IP
XX000000
P3
11111111
IE
0X000000
P2
11111111
SCON
00000000
P1
11111111
TCON
00000000
P0
11111111
SBUF
XXXXXXXX
TMOD
00000000
TL0
00000000
SP
00000111
DPL
00000000
AT89C52
TL1
00000000
DPH
00000000
TH0
00000000
TH1
00000000
0BFH
0B7H
0AFH
0A7H
9FH
97H
8FH
PCON
0XXX0000
87H