AT89C51ID2-SMSIM ATMEL [ATMEL Corporation], AT89C51ID2-SMSIM Datasheet - Page 14

• Manufacturer Part Number: AT89C51ID2-SMSIM
• Description: 8-bit Flash Microcontroller
• Manufacturer: ATMEL [ATMEL Corporation]

Table 14. Pin Description (Continued)
14
PI2.0 - PI2.1
RST
ALE/PROG
PSEN
EA
Mnemonic
AT89C51ID2
PLCC44
34, 12
34
12
10
33
32
35
VQFP44
28, 6
6
28
27
26
29
4
Pin Number
PLCC68
1, 36
36
30
68
67
1
2
VQFP64
57, 26
57
26
21
56
55
58
Type
O (I)
I/O
I/O
O
I
I
Name and Function
Port I2: Port I2 is an open drain. It can be used as inputs (must be polar-
ized to Vcc with external resistor to prevent any parasitic current consump-
tion).
SCL (PI2.0): 2-wire Serial Clock
SCL output the serial clock to slave peripherals
SCL input the serial clock from master
SDA (PI2.1): 2-wire Serial Data
SDA is the bidirectional 2-wire data line
Reset: A high on this pin for two machine cycles while the oscillator is run-
ning, resets the device. An internal diffused resistor to V
on reset using only an external capacitor to V
the hardware watchdog forces a system reset.
Address Latch Enable/Program Pulse: Output pulse for latching the low
byte of the address during an access to external memory. In normal opera-
tion, ALE is emitted at a constant rate of 1/6 (1/3 in X2 mode) the oscillator
frequency, and can be used for external timing or clocking. Note that one
ALE pulse is skipped during each access to external data memory. This pin
is also the program pulse input (PROG) during Flash programming. ALE
can be disabled by setting SFR’s AUXR.0 bit. With this bit set, ALE will be
inactive during internal fetches.
Program Strobe ENable: The read strobe to external program memory.
When executing code from the external program memory, PSEN is acti-
vated twice each machine cycle, except that two PSEN activations are
skipped during each access to external data memory. PSEN is not acti-
vated during fetches from internal program memory.
External Access Enable: EA must be externally held low to enable the
device to fetch code from external program memory locations 0000H to
FFFFH. If security level 1 is programmed, EA will be internally latched on
Reset.
CC
. This pin is an output when
SS
permits a power-
4289A–8051–09/03