On Tue, 29 Apr 2003 16:14:26 +0200, you wrote:

>Mike Harrison wrote:
>> Use HCMOS instead - LSTTL is completely obsolete, as HCMOS
>> is better in all respects (speed, power, cost).
>
>Is that so ?
>Power yes, cost maybe, but speed ?

>>From what I'v seen bipolar 74xxx is still faster then CMOS 74xxx.
My Philips  HCMOS book says Typ. 8ns max 18ns for HC00 at 4.5V (probably =
a ns or so better at 5V)
My TI TTL book says Typ 11 max 22, typ 7 max 15 for rising and falling =
edges respectively

HCMOS has faster, and more symmetrical rise/fall times, and much better =
drive

LS is obsolete and there is no good reason to be designing it into new =
products.
 If you are within a few ns of your product working or not you should be =
using the logic family with
the next speed up (i.e. 74AC).=20


>>From the "Texas Digital Logic Pocket Data Bbook" :
>
>74xx00, switching time (low to high):
>
>7400    :  22   ns
>74LS00  :  15   ns
>74ALS0  :  11   ns
>74AS00  :   4.5 ns
>74F00   :   6   ns
>
>74HC00  :  25   ns

>74HCT00 :  30   ns
>74ACT   :  12.3 ns
>
>Jan-Erik S=F6derholm

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