AUTOMOTIVE MICROCONTROLLER MCS 51
Diagrams are for pin reference only Package sizes are not to scale
270499 – 3
EPROM only
Pin (DIP)
Figure 3 MCS 51 Microcontroller Connections
Port 1
Port 1 is an 8-bit bidirectional I O port with internal
pullups The Port 1 output buffers can sink source 4
LS TTL inputs Port 1 pins that have 1s written to
them are pulled high by the internal pullups and in
that state can be used as inputs As inputs Port 1
pins that are externally pulled low will source current
(I
IL
on the datasheet) because of the internal pull-
ups
Port 1 also receives the low-order address bytes
during program verification of the ROM
In the 8032AH and 8052AH Port 1 pins P1 0 and
P1 1 also serve the T2 and T2EX functions respec-
tively
uses strong internal pullups when emitting 1s Dur-
ing accesses to external Data Memory that use 8-bit
addresses (MOVX Ri) Port 2 emits the contents of
the P2 Special Function Register
Port 2 also receives the high-order address bits dur-
ing program verification of the ROM
Port 3
Port 3 is an 8-bit bidirectional I O port with internal
pullups The Port 3 output buffers can sink source 4
LS TTL inputs Port 3 pins that have 1s written to
them are pulled high by the internal pullups and in
that state can be used as inputs As inputs Port 3
pins that are externally pulled low will source current
(I
IL
on the datasheet) because of the pullups
Port 3 also serves the functions of various special
features of the MCS 51 microcontroller family as
listed below
Port
Pin
P3 0
P3 1
P3 2
P3 3
P3 4
P3 5
P3 6
P3 7
Alternative Function
RXD (serial input port)
TXD (serial output port)
INT0 (external interrupt 0)
INT1 (external interrupt 1)
T0 (Timer 0 external input)
T1 (Timer 1 external input)
WR (external data memory write strobe)
RD (external data memory read strobe)
Port 2
Port 2 is an 8-bit bidirectional I O port with internal
pullups The Port 2 output buffers can sink source 4
LS TTL inputs Port 2 pins that have 1s written to
them are pulled high by the internal pullups and in
that state can be used as inputs As inputs Port 2
pins that are externally pulled low will source current
(I
IL
on the datasheet) 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
4
INTEL [ INTEL CORPORATION ]
