Pin Description
VCC
GND
Supply voltage (all packages except 42-PDIP).
Ground (all packages except 42-PDIP; for 42-PDIP GND connects only the logic core and the
embedded program memory).
VDD
Supply voltage for the 42-PDIP which connects only the logic core and the embedded program
memory.
PWRVDD
PWRGND
Supply voltage for the 42-PDIP which connects only the I/O Pad Drivers. The application
board MUST connect both VDD and PWRVDD to the board supply voltage.
Ground for the 42-PDIP which connects only the I/O Pad Drivers. PWRGND and GND are
weakly connected through the common silicon substrate, but not through any metal link. The
application board MUST connect both GND and PWRGND to the board ground.
Port 0
Port 0 is an 8-bit open drain bi-directional I/O port. As an output port, each pin can sink eight
TTL inputs. When 1s are written to port 0 pins, the pins can be used as high-impedance
inputs.
Port 0 can also be configured to be the multiplexed low-order address/data bus during
accesses to external program and data memory. In this mode, P0 has internal pull-ups.
Port 0 also receives the code bytes during Flash programming and outputs the code bytes
during program verification. External pull-ups are required during program verification.
Port 1
Port 1 is an 8-bit bi-directional I/O port with internal pull-ups. The Port 1 output buffers can
sink/source four TTL inputs. When 1s are written to Port 1 pins, they are pulled high by the
internal pull-ups and can be used as inputs. As inputs, Port 1 pins that are externally being
pulled low will source current (IIL) because of the internal pull-ups.
Port 1 also receives the low-order address bytes during Flash programming and verification.
Port Pin
P1.5
Alternate Functions
MOSI (used for In-System Programming)
MISO (used for In-System Programming)
SCK (used for In-System Programming)
P1.6
P1.7
Port 2
Port 2 is an 8-bit bi-directional I/O port with internal pull-ups. The Port 2 output buffers can
sink/source four TTL inputs. When 1s are written to Port 2 pins, they are pulled high by the
internal pull-ups and can be used as inputs. As inputs, Port 2 pins that are externally being
pulled low will source current (IIL) 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, Port 2 uses strong internal pull-ups when emitting 1s. During accesses to external
data memory that use 8-bit addresses (MOVX @ RI), Port 2 emits the contents of the P2 Spe-
cial Function Register.
Port 2 also receives the high-order address bits and some control signals during Flash pro-
gramming and verification.
4
AT89S51
2487B–MICRO–12/03
ATMEL [ ATMEL ]
