DS87C520/DS83C520 EPROM/ROM High-Speed Microcontrollers

32 of 45

AC ELECTRICAL CHARACTERISTICS (Note 1)

33 MHz

VARIABLE CLOCK

PARAMETER

SYMBOL

MIN

MAX

MIN

MAX

UNITS

External Oscillator

0

33

0

33

Oscillator

Frequency

External Crystal

1

33

1

33

MHz

ALE Pulse Width

40

ns

Port 0 Address Valid to ALE Low

10

ns

Address Hold after ALE Low

(Note 2)

(Note 2)

ns

ALE Low to Valid Instruction In

43

ns

4

ns

PSEN

Pulse Width

55

ns

PSEN

Low to Valid Instruction In

37

ns

0

0

ns

26

ns

Port 0 Address to Valid Instruction In

59

ns

Port 2 Address to Valid Instruction In

68

ns

PSEN

Low to Address Float

(Note 2)

(Note 2)

ns

Note 1:

All parameters apply to both commercial and industrial temperature range operation unless otherwise noted.

Specifications to -40°C are guaranteed by design and are not production tested. AC electrical characteristics are not

100% tested, but are characterized and guaranteed by design. All signals characterized with load capacitance of 80pF

except Port 0, ALE,

PSEN, RD, and WR with 100pF. Interfacing to memory devices with float times (turn off times)

over 25ns may cause contention. This will not damage the parts, but will cause an increase in operating current.

Specifications assume a 50% duty cycle for the oscillator. Port 2 and ALE timing will change in relation to duty cycle

variation.

Note 2:

Address is driven strongly until ALE falls, and is then held in a weak latch until overdriven externally.