80C51FA Datasheet, PDF (5/13 Pages) Intel Corporation – EVENT-CONTROL CHMOS SINGLE-CHIP 8-BIT MICROCONTROLLER

AUTOMOTIVE 80C51FA 83C51FA
addresses (MOVX Ri) Port 2 emits the contents of
the P2 Special Function Register
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 datasheet) because of the pullups
Port 3 also serves the functions of various special
features of the MCS 51 microcontroller family as
listed below
EA V_PP External Access enable EA must be
strapped to V_SS in order to enable the device to
fetch code from external Program Memory locations
0000H to 0FFFFH Note however that if either of
the Program Lock bits are programmed EA will be
internally latched on reset
EA should be strapped to V_CC for internal program
executions
XTAL1 Input to the inverting oscillator amplifier
XTAL2 Output from the inverting oscillator amplifi-
er
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)
RESET Reset input A high on this pin for two ma-
chine cycles while the oscillator is running resets the
device An internal pulldown resistor permits a pow-
er-on reset with only a capacitor connected to V_CC
ALE PROG Address Latch Enable output pulse for
latching the low byte of the address during accesses
to external memory
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
Throughout the remainder of this datasheet ALE will
refer to the signal coming out of the ALE PROG pin
and the pin will be referred to as the ALE PROG pin
PSEN Program Store Enable is the read strobe to
external Program Memory
When the 83C51FA is executing code from external
Program Memory PSEN is activated twice each ma-
chine cycle except that two PSEN activations are
skipped during each access to external Data Memo-
ry
OSCILLATOR CHARACTERISTICS
XTAL1 and XTAL2 are the input and output respec-
tively of a inverting amplifier which can be config-
ured for use as an on-chip oscillator as shown in
Figure 4 Either a quartz crystal or ceramic resonator
may be used More detailed information concerning
the use of the on-chip oscillator is available in Appli-
cation Note AP-155 ‘‘Oscillators for Microcontrol-
lers ’’
To drive the device from an external clock source
XTAL1 should be driven while XTAL2 floats as
shown in Figure 5 There are no requirements on the
duty cycle of the external clock signal since the in-
put to the internal clocking circuitry is through a di-
vide-by-two flip-flop but minimum and maximum
high and low times specified on the datasheet must
be observed
An external oscillator may encounter as much as a
100 pF load at XTAL1 when it starts up This is due
to interaction between the amplifier and its feedback
capacitance Once the external signal meets the V_IL
and V_IH specifications the capacitance will not ex-
ceed 20 pF
270501 – 5
C1 C2 e 30 pF g10 pF for Crystals
For Ceramic Resonators contact resonator manufacturer
Figure 4 Oscillator Connections
5