AT89S52
weakly pulled high. Setting the ALE-disable bit has no
effect if the microcontroller is in external execution mode.
Note, however, that if lock bit 1 is programmed, EA will be
internally latched on reset.
EA should be strapped to VCC for internal program execu-
tions.
PSEN
Program Store Enable (PSEN) is the read strobe to exter-
nal program memory.
This pin also receives the 12-volt programming enable volt-
age (VPP) during Flash programming.
When the AT89S52 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.
XTAL1
Input to the inverting oscillator amplifier and input to the
internal clock operating circuit.
EA/VPP
XTAL2
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.
Output from the inverting oscillator amplifier.
Table 1. AT89S52 SFR Map and Reset Values
0F8H
0FFH
0F7H
0EFH
0E7H
0DFH
0D7H
B
0F0H
00000000
0E8H
ACC
0E0H
00000000
0D8H
PSW
0D0H
00000000
T2CON
00000000
T2MOD
XXXXXX00
RCAP2L
00000000
RCAP2H
00000000
TL2
00000000
TH2
00000000
0C8H
0C0H
0B8H
0B0H
0A8H
0A0H
98H
0CFH
0C7H
0BFH
0B7H
0AFH
0A7H
9FH
IP
XX000000
P3
11111111
IE
0X000000
P2
11111111
AUXR1
XXXXXXX0
WDTRST
XXXXXXXX
SCON
00000000
SBUF
XXXXXXXX
P1
11111111
90H
97H
TCON
00000000
TMOD
00000000
TL0
00000000
TL1
00000000
TH0
00000000
TH1
00000000
AUXR
XXX00XX0
88H
8FH
P0
11111111
SP
00000111
DP0L
00000000
DP0H
00000000
DP1L
00000000
DP1H
00000000
PCON
0XXX0000
80H
87H
5
ATMEL [ ATMEL ]
