80C52 Datasheet, PDF (4/23 Pages) Intel Corporation – CHMOS SINGLE-CHIP 8-BIT MICROCONTROLLER

8XC52 54 58
PIN DESCRIPTIONS
V_CC Supply voltage
V_SS Circuit ground
V_SS1 Secondary ground (not on DIP) Provided to
reduce ground bounce and improve power supply
by-passing
NOTE
This pin is not a substitute for the V_SS pin (pin 22)
(Connection not necessary for proper operation )
Port 0 Port 0 is an 8-bit open drain bidirectional
I O port As an output port each pin can sink several
LS TTL inputs Port 0 pins that have 1’s written to
them float and in that state can be used as high-im-
pedance inputs
Port 0 is also the multiplexed low-order address and
data bus during accesses to external Program and
Data Memory In this application it uses strong inter-
nal pullups when emitting 1’s and can source and
sink several LS TTL inputs
Port 0 also receives the code bytes during EPROM
programming and outputs the code bytes during
program verification External pullup resistors are re-
quired during program verification
Port 1 Port 1 is an 8-bit bidirectional I O port with
internal pullups The Port 1 output buffers can drive
LS TTL inputs Port 1 pins that have 1’s 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 data sheet) because of the internal pull-
ups
In addition Port 1 serves the functions of the follow-
ing special features of the 8XC5X
Port Pin
P1 0
P1 1
Alternate Function
T2 (External Count Input to Timer
Counter 2) Clock-Out
T2EX (Timer Counter 2 Capture
Reload Trigger and Direction Control)
Port 1 receives the low-order address bytes during
EPROM programming and verifying
Port 2 Port 2 is an 8-bit bidirectional I O port with
internal pullups The Port 2 output buffers can drive
LS TTL inputs Port 2 pins that have 1’s 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 data sheet) 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 pullups when emitting 1’s 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
Some Port 2 pins receive the high-order address bits
during EPROM programming and program verifica-
tion
Port 3 Port 3 is an 8-bit bidirectional I O port with
internal pullups The Port 3 output buffers can drive
LS TTL inputs Port 3 pins that have 1’s 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 data sheet) because of the pullups
Port 3 also serves the functions of various special
features of the 8051 Family as listed below
Port Pin
Alternate Function
P3 0
P3 1
P3 2
P3 3
P3 4
P3 5
P3 6
P3 7
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)
RST Reset input A high on this pin for two machine
cycles while the oscillator is running resets the de-
vice The port pins will be driven to their reset condi-
tion when a minimum V_IHI voltage is applied whether
the oscillator is running or not An internal pulldown
resistor permits a power-on reset with only a capaci-
tor connected to V_CC
ALE Address Latch Enable output pulse for latching
the low byte of the address during accesses to ex-
ternal memory This pin (ALE PROG) is also the
program pulse input during EPROM programming for
the 87C5X
In normal operation ALE is emitted at a constant
rate of the oscillator frequency and may be used
for external timing or clocking purposes Note how-
ever that one ALE pulse is skipped during each ac-
cess to external Data Memory
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