21

AT89S51

2487A–10/01

AC Characteristics

Under operating conditions, load capacitance for Port 0, ALE/PROG, and PSEN = 100 pF; load capacitance for all other

outputs = 80 pF.

External Program and Data Memory Characteristics

Symbol

Parameter

12 MHz Oscillator

Variable Oscillator

Units

Min

Max

Min

Max

Oscillator Frequency

0

33

MHz

t

LHLL

ALE Pulse Width

127

2t

ns

t

AVLL

Address Valid to ALE Low

43

t

ns

Address Hold After ALE Low

48

ns

t

LLIV

ALE Low to Valid Instruction In

233

4t

ns

t

LLPL

ALE Low to PSEN Low

43

t

ns

PSEN Pulse Width

205

ns

t

PLIV

PSEN Low to Valid Instruction In

145

3t

ns

t

PXIX

Input Instruction Hold After PSEN

00

ns

Input Instruction Float After PSEN

59

ns

t

PXAV

PSEN to Address Valid

75

t

ns

t

AVIV

Address to Valid Instruction In

312

5t

ns

PSEN Low to Address Float

10

10

ns

t

RLRH

RD Pulse Width

400

6t

ns

t

WLWH

WR Pulse Width

400

6t

ns

RD Low to Valid Data In

252

ns

t

RHDX

Data Hold After RD

00

ns

t

RHDZ

Data Float After RD

97

2t

ns

ALE Low to Valid Data In

517

ns

t

AVDV

Address to Valid Data In

585

9t

ns

t

LLWL

ALE Low to RD or WR Low

200

300

3t

3t

ns

Address to RD or WR Low

203

ns

t

QVWX

Data Valid to WR Transition

23

t

ns

t

QVWH

Data Valid to WR High

433

7t

ns

Data Hold After WR

33

ns

t

RLAZ

RD Low to Address Float

0

0

ns

t

WHLH

RD or WR High to ALE High

43

123

t

t

ns