AT89C51

4-38

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

16 to 24 MHz Oscillator

Units

Min

Max

Min

Max

Oscillator Frequency

0

24

MHz

ALE Pulse Width

127

ns

Address Valid to ALE Low

43

ns

Address Hold After ALE Low

48

ns

ALE Low to Valid Instruction In

233

ns

ALE Low to PSEN Low

43

ns

PSEN Pulse Width

205

ns

PSEN Low to Valid Instruction In

145

ns

Input Instruction Hold After PSEN

00

ns

Input Instruction Float After PSEN

59

ns

PSEN to Address Valid

75

ns

Address to Valid Instruction In

312

ns

PSEN Low to Address Float

10

10

ns

RD Pulse Width

400

ns

WR Pulse Width

400

ns

RD Low to Valid Data In

252

ns

Data Hold After RD

00

ns

Data Float After RD

97

ns

ALE Low to Valid Data In

517

ns

Address to Valid Data In

585

ns

ALE Low to RD or WR Low

200

300

ns

Address to RD or WR Low

203

ns

Data Valid to WR Transition

23

ns

Data Valid to WR High

433

ns

Data Hold After WR

33

ns

RD Low to Address Float

0

0

ns

RD or WR High to ALE High

43

123

ns