
12
4235K–8051–05/08
AT89C51RD2/ED2
9
3
29
20
I/O
P1.7: Input/Output:
I/O
CEX4: Capture/Compare External I/O for PCA module 4
I/O
MOSI: SPI Master Output Slave Input line
When SPI is in master mode, MOSI outputs data to the slave peripheral.
When SPI is in slave mode, MOSI receives data from the master
controller.
XTALA1
21
15
49
38
I
XTALA 1: Input to the inverting oscillator amplifier and input to the
internal clock generator circuits.
XTALA2
20
14
48
37
O
XTALA 2: Output from the inverting oscillator amplifier
P2.0 - P2.7
24 - 31
18 - 25
54, 55,
56, 58,
59, 61,
64, 65
43, 44,
45, 47,
48, 50,
53, 54
I/O
Port 2: Port 2 is an 8-bit bidirectional I/O port with internal pull-ups. Port 2
pins that have 1s written to them are pulled high by the internal pull-ups
and can be used as inputs. As inputs, Port 2 pins that are externally
pulled low will source current because of the internal pull-ups. Port 2
emits the high-order address byte during fetches from external program
memory and during accesses to external data memory that use 16-bit
addresses (MOVX @DPTR).In this application, it uses strong internal
pull-ups emitting 1s. During accesses to external data memory that use
8-bit addresses (MOVX @Ri), port 2 emits the contents of the P2 SFR.
P3.0 - P3.7
11,
13 - 19
5,
7 - 13
34, 39,
40, 41,
42, 43,
45, 47
25, 28,
29, 30,
31, 32,
34, 36
I/O
Port 3: Port 3 is an 8-bit bidirectional I/O port with internal pull-ups. Port 3
pins that have 1s written to them are pulled high by the internal pull-ups
and can be used as inputs. As inputs, Port 3 pins that are externally
pulled low will source current because of the internal pull-ups. Port 3 also
serves the special features of the 80C51 family, as listed below.
11
5
34
25
I
RXD (P3.0): Serial input port
13
7
39
28
O
TXD (P3.1): Serial output port
14
8
40
29
I
INT0 (P3.2): External interrupt 0
15
9
41
30
I
INT1 (P3.3): External interrupt 1
16
10
42
31
I
T0 (P3.4): Timer 0 external input
17
11
43
32
I
T1 (P3.5): Timer 1 external input
18
12
45
34
O
WR (P3.6): External data memory write strobe
19
13
47
36
O
RD (P3.7): External data memory read strobe
P4.0 - P4.7
-
20, 24,
26, 44,
46, 50,
53, 57
11, 15,
17,33,
35,39,
42, 46
I/O
Port 4: Port 4 is an 8-bit bidirectional I/O port with internal pull-ups. Port 3
pins that have 1s written to them are pulled high by the internal pull-ups
and can be used as inputs. As inputs, Port 3 pins that are externally
pulled low will source current because of the internal pull-ups.
P5.0 - P5.7
-
60, 62,
63, 7, 8,
10, 13, 16
49, 51,
52, 62,
63, 1, 4, 7
I/O
Port 5: Port 5 is an 8-bit bidirectional I/O port with internal pull-ups. Port 3
pins that have 1s written to them are pulled high by the internal pull-ups
and can be used as inputs. As inputs, Port 3 pins that are externally
pulled low will source current because of the internal pull-ups.
RST
10
4
30
21
I
Reset: A high on this pin for two machine cycles while the oscillator is
running, resets the device. An internal diffused resistor to VSS permits a
power-on reset using only an external capacitor to V
CC. This pin is an
output when the hardware watchdog forces a system reset.
Table 4-1.
Pin Description (Continued)
Mnemonic
Pin Number
Type
Name and Function
PLCC44 VQFP44
PLCC68
VQFP64