87C51F Intel Corporation, 87C51F Datasheet - Page 5

• Manufacturer Part Number: 87C51F
• Description: CHMOS SINGLE-CHIP 8-BIT MICROCONTROLLER
• Manufacturer: Intel Corporation

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
uses strong internal pullups when emitting 1’s Dur-
ing accesses to external Data Memory that use 8-bit
addresses (MOVX
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
Port 3 also serves the functions of various special
features of the MCS-51 Family as listed below
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
oscillator is running or not An internal pulldown re-
sistor permits a power-on reset with only a capacitor
connected to V
ALE PROG Address Latch Enable output pulse for
latching the low byte of the address during accesses
to external memory This pin (ALE PROG) is also
the program pulse input during EPROM program-
ming for the 87C51FA FB FC
Port Pin
IL
P3 0
P3 1
P3 2
P3 3
P3 4
P3 5
P3 6
P3 7
on the data sheet) because of the pullups
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)
CC
Alternate Function
Ri) Port 2 emits the contents
DPTR) In this application it
IH1
is applied whether the
Design for Microcontrollers’’
In normal operation ALE is emitted at a constant
rate of
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 data sheet 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 87C51FA FB FC is executing code from
external Program Memory PSEN is activated twice
each machine cycle except that two PSEN activa-
tions are skipped during each access to external
Data Memory
EA V
strapped to V
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
executions
This pin also receives the programming supply volt-
age (V
XTAL1 Input to the inverting oscillator amplifier
XTAL2 Output from the inverting oscillator amplifier
OSCILLATOR CHARACTERISTICS
XTAL1 and XTAL2 are the input and output respec-
tively of an 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’’ and in Application Note AP-486 ‘‘Oscillator
PP
AUTOMOTIVE 87C51FA FB FC FC-20
PP
) during EPROM programming
the oscillator frequency and may be used
External Access enable EA must be
SS
in order to enable the device to
CC
for internal program
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