87C5180C51BH80C31BH

EXPLANATION OF THE AC SYMBOLS

Each timing symbol has 5 characters The first char-

acter is always a ‘T’ (stands for time) The other

characters depending on their positions stand for

the name of a signal or the logical status of that

signal The following is a list of all the characters and

what they stand for

AAddress

CClock

DInput data

HLogic level HIGH

IInstruction (program memory contents)

LLogic level LOW or ALE

PPSEN

QOutput data

RRD signal

TTime

VValid

WWR signal

XNo longer a valid logic level

ZFloat

For example

TAVLL e Time from Address Valid to ALE Low

TLLPL e Time from ALE Low to PSEN Low

AC CHARACTERISTICS

(Over Operating Conditions Load Capacitance for Port 0 ALE and

PSEN e 100 pF Load Capacitance for All Other Outputs e 80 pF)

EXTERNAL MEMORY CHARACTERISTICS

All parameter values apply to all devices unless otherwise indicated In this table 87C51BH refers to

87C51BH 87C51-1BH-1 and 87C51-2BH-2

Symbol

Parameter

Oscillator

Units

12 MHz

24 MHz

Variable

Min

Max

Min

Max

Min

Max

1TCLCL

Oscillator Frequency

87C51BH

35

12

MHz

87C51-1BH-1

35

16

MHz

87C51-2BH-2

05

12

MHz

87C51-24BH-24

35

24

MHz

TLHLL

ALE Pulse Width

127

43

2TCLCLb40

ns

TAVLL

Address Valid to ALE Low

87C51BH

43

TCLCLb40

ns

87C51-24BH-24

12

TCLCLb30

ns

TLLAX

Address Hold After ALE Low

53

12

TCLCLb30

ns

TLLIV

ALE Low to Valid Instr In

87C51BH

234

4TCLCLb100

ns

87C51-24BH-24

91

4TCLCLb75

ns

TLLPL

ALE Low to PSEN Low

53

12

TCLCLb30

ns

TPLPH

PSEN Pulse Width

205

80

3TCLCLb45

ns

TPLIV

PSEN Low to Valid Instr In

87C51BH

145

3TCLCLb105

ns

87C51-24BH-24

35

3TCLCLb90

ns

12