Mnemonic
Type
Name and Function
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.
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.
External Access Enable:
EA must be externally held low to enable the
device to fetch code from external program memory locations.
Crystal 1:
Input to the inverting oscillator amplifier and input to the
internal clock generator circuits.
Crystal 2:
Output from the inverting oscillator amplifier
ALE
O (I)
PSEN
O
EA
XTAL1
XTAL2
I
I
O
4
80C32E
4149N–AERO–04/07
ATMEL [ ATMEL CORPORATION ]
