SN74ALS232B

16

× 4 ASYNCHRONOUS FIRST-IN, FIRST-OUT MEMORY

SCAS251B – FEBRUARY 1989 – REVISED APRIL 1998

6

POST OFFICE BOX 655303

timing requirements over recommended operating free-air temperature range (see Figure 1)

MIN

NOM

MAX

UNIT

f

†

Clock frequency

LDCK

40

MHz

fclock†

Clock frequency

UNCK

40

MHz

RST low

18

LDCK low

15

tw

Pulse duration

LDCK high

10

ns

UNCK low

15

UNCK high

10

t

Setup time

Data before LDCK

↑

8

ns

tsu

Setup time

LDCK inactive before RST

↑

5

ns

th

Hold time

Data after LDCK

↑

5

ns

th

Hold time

LDCK inactive after RST

↑

5

ns

† The maximum possible clock frequency is 40 MHz. The maximum clock frequency when using a 50% duty cycle is 33.3 MHz.

switching characteristics (see Figure 1)

PARAMETER

FROM

(INPUT)

TO

(OUTPUT)

MIN

TYP‡

MAX

MIN

MAX

UNIT

fmax

LDCK, UNCK

50

40

MHz

t d

LDCK

↑

Any Q

14

23

6

30

ns

tpd

UNCK

↑

Any Q

15

23

6

30

ns

tPLH

LDCK

↑

EMPTY

13

20

5

25

ns

UNCK

↑

EMPTY

15

22

6

27

tPHL

RST

↓

EMPTY

15

21

5

26

ns

LDCK

↑

FULL

15

22

6

27

tPLH

UNCK

↑

FULL

13

20

5

25

ns

tPLH

RST

↓

FULL

16

23

7

28

ns

ten

OE

↑

Q

5

12

1

14

ns

tdis

OE

↓

Q

5

12

1

16

ns

‡ Typical values at VCC – 5 V, TA = 25°C.