87C54 Datasheet, PDF (5/20 Pages) Intel Corporation – CHMOS SINGLE-CHIP 8-BIT MICROCONTROLLER WITH 16 KBYTES USER PROGRAMMABLE EPROM

AUTOMOTIVE 87C54 87C54-20
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 MCS-51 Family as listed below
Port Pin
P3 0
P3 1
P3 2
P3 3
P3 4
P3 5
P3 6
P3 7
Alternate 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)
In addition some Port 3 pins receive the high-order
address bits and act as control signals during
EPROM programming and programming verification
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_IH1 is applied whether the
oscillator is running or not An internal pulldown re-
sistor permits a power-on reset with only a capacitor
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 87C54
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 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 87C54 is executing code from external
Program Memory PSEN is activated twice each
machine cycle except that two PSEN activations
are skipped during each access to external Data
Memory
EA V_PP External Access enable EA must be
strapped to VSS in order to enable the device to
fetch code from external Program Memory locations
0000H to 0FFFFH Note however that if any of the
Lock bits are programmed EA will be internally
latched on reset
EA should be strapped to V_CC for internal program
executions
This pin also receives the programming supply volt-
age (V_PP) during EPROM programming
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 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 ’’
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