EN87C51FA1SF76 Ver la hoja de datos (PDF) - Atmel Corporation

Número de pieza

componentes Descripción

Fabricante

EN87C51FA1SF76

CHMOS SINGLE-CHIP 8-BIT MICROCONTROLLER

Atmel Corporation 

87C51/80C51BH/80C31BH

In normal operation ALE is emitted at a constant

rate of 1/6 the oscillator frequency, and may be

used for external timing or clocking purposes. Note,

however, that one ALE pulse is skipped during each

access to external Data Memory.

PSEN: Program Store Enable is the Read strobe to

External Program Memory. When the 87C51/BH is

executing from Internal Program Memory, PSEN is

inactive (high). When the device 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 Exter-

nal Data Memory.

EA/V PP: External Access enable. EA must be

strapped to VSS in order to enable the 87C51/BH to

fetch code from External Program Memory locations

starting at 0000H up to FFFFH. Note, however, that

if either of the Lock Bits is programmed, the logic

level at EA is internally latched during reset.

EA must be strapped to VCC for internal program

execution.

This pin also receives the programming supply volt-

age (VPP) during EPROM programming.

XTAL1 : Input to the inverting oscillator amplifier.

XTAL2 : Output from the inverting oscillator amplifi-

er.

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 3.

To drive the device from an external clock source,

XTAL1 should be driven, while XTAL2 is left uncon-

nected, as shown in Figure 4. There are no require-

ments on the duty cycle of the external clock signal,

since the input to the internal clocking circuitry is

through a divide-by-two flip-flop, but minimum and

maximum high and low times specified on the data

sheet 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 VIL

and VIH specifications the capacitance will not ex-

ceed 20 pF.

272335 ±6

Figure 4. External Clock Drive

272335 ±5

Figure 3. Using the On-Chip Oscillator

5

Share Link: