AT89C51ED2-RDTUM datasheet(11/137 Pages) ATMEL

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4235K–8051–05/08

AT89C51RD2/ED2

Table 4-1.

Pin Description

Mnemonic

Pin Number

Type

Name and Function

PLCC44 VQFP44

PLCC68

VQFP64

VSS

Ground: 0V reference

Power Supply: This is the power supply voltage for normal, idle and

power-down operation

P0.0 - P0.7

43 - 36

37 - 30

15, 14,

12, 11,

9,6, 5, 3

6, 5, 3, 2,

64,

61,60,59

I/O

Port 0: Port 0 is an open-drain, bidirectional I/O port. Port 0 pins that

have 1s written to them float and can be used as high impedance inputs.

Port 0 must be polarized to VCC or VSS in order to prevent any parasitic

current consumption. Port 0 is also the multiplexed low-order address

and data bus during access to external program and data memory. In this

application, it uses strong internal pull-up when emitting 1s. Port 0 also

inputs the code bytes during EPROM programming. External pull-ups are

required during program verification during which P0 outputs the code

bytes.

P1.0 - P1.7

2 - 9

40 - 44

1 - 3

19, 21,

22, 23,

25, 27,

28, 29

10, 12,

13, 14,

16, 18,

19, 20

I/O

Port 1: Port 1 is an 8-bit bidirectional I/O port with internal pull-ups. Port 1

pins that have 1s written to them are pulled high by the internal pull-ups

and can be used as inputs. As inputs, Port 1 pins that are externally

pulled low will source current because of the internal pull-ups. Port 1 also

receives the low-order address byte during memory programming and

verification.

Alternate functions for AT89C51RD2/ED2 Port 1 include:

I/O

P1.0: Input/Output

I/O

T2 (P1.0): Timer/Counter 2 external count input/Clockout

I/O

P1.1: Input/Output

T2EX: Timer/Counter 2 Reload/Capture/Direction Control

SS: SPI Slave Select

I/O

P1.2: Input/Output

ECI: External Clock for the PCA

I/O

P1.3: Input/Output

I/O

CEX0: Capture/Compare External I/O for PCA module 0

I/O

P1.4: Input/Output

I/O

CEX1: Capture/Compare External I/O for PCA module 1

I/O

P1.5: Input/Output

I/O

CEX2: Capture/Compare External I/O for PCA module 2

I/O

MISO: SPI Master Input Slave Output line

When SPI is in master mode, MISO receives data from the slave

peripheral. When SPI is in slave mode, MISO outputs data to the master

controller.

I/O

P1.6: Input/Output

I/O

CEX3: Capture/Compare External I/O for PCA module 3

I/O

SCK: SPI Serial Clock

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