AT89S8253-24JC datasheet(5/56 Pages) ATMEL

5 / 56 page

AT89S8253 [Preliminary]

3286A–MICRO–7/04

If desired, ALE operation can be disabled by setting bit 0 of the AUXR SFR at location 8EH.

With the bit set, ALE is active only during a MOVX or MOVC instruction. Otherwise, the pin is

weakly pulled high. Setting the ALE-disable bit has no effect if the microcontroller is in external

execution mode.

PSEN

Program Store Enable. PSEN is the read strobe to external program memory (active low).

When the AT89S8253 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/VPP

External Access Enable. EA must be strapped to GND in order to enable the device to fetch

code from external program memory locations starting at 0000H up to FFFFH. Note, however,

that if lock bit 1 is programmed, EA will be internally latched on reset.

EA should be strapped to V

CC for internal program executions. This pin also receives the

12-volt programming enable voltage (V

PP) during Flash programming when 12-volt program-

ming is selected.

XTAL1

Input to the inverting oscillator amplifier and input to the internal clock operating circuit.

XTAL2

Output from the inverting oscillator amplifier.

AT89S8253-24JC Datasheet(PDF) 5 Page - ATMEL Corporation