4

80C32E

4149M–AERO–06/04

ALE

O (I)

Address Latch Enable: Output pulse for latching the low byte of the

address during an access to external memory. In normal operation, ALE

is emitted at a constant rate of 1/6 the oscillator frequency, and can be

used for external timing or clocking. Note that one ALE pulse is skipped

during each access to external data memory.

PSEN

O

Program Store ENable: The read strobe to external program memory.

When executing code from the external program memory, PSEN is

activated twice each machine cycle, except that two PSEN activations

are skipped during each access to external data memory. PSEN is not

activated during fetches from internal program memory.

EA

I

External Access Enable: EA must be externally held low to enable the

device to fetch code from external program memory locations.

XTAL1

I

Crystal 1: Input to the inverting oscillator amplifier and input to the

internal clock generator circuits.

XTAL2

O

Crystal 2: Output from the inverting oscillator amplifier

Mnemonic

Type

Name and Function