74HC series Fanout into AT28C256

[PAUL BAAS]

Hi friends,

I need to feed a signal from one 74HC273 flip flop into 15 of the eeproms part number AT28C256.

I need to know if it;s fine for me to directly feed the signals into 15 AT28C256 at once ?

Or should I divide the signals into 2 parts and feed each into a 244, and then from the 244 into 7 and 8 of the AT28C256 each ?

In other words, can the 273 cope with feeding 15 AT28C256 ?

From what I know 74HC has virtually infinite fanout into CMOS, and the AT28C256 are CMOS.

Thanks!

 

[gophert]

Hi friends,

I need to feed a signal from one 74HC273 flip flop into 15 of the eeproms part number AT28C256.

I need to know if it;s fine for me to directly feed the signals into 15 AT28C256 at once ?

Or should I divide the signals into 2 parts and feed each into a 244, and then from the 244 into 7 and 8 of the AT28C256 each ?

In other words, can the 273 cope with feeding 15 AT28C256 ?

From what I know 74HC has virtually infinite fanout into CMOS, and the AT28C256 are CMOS.

Thanks!

The cmos inputs are not drawing any current from the 74HC chip on a continuous basis but there is come capacitance on the cmos so it take a few nanoseconds to charge. Now, multiply the few nanoseconds into 244x more capacitance and you'll see that you run into switching speed issues. A high may not have enough time to go high in one clock cycle (depending on frequency).

Good luck.

 

[PAUL BAAS]

I didn't say 244 cmos gates............its only 15

 

[gophert]

I didn't say 244 cmos gates............its only 15

Sorry, you'll be fine.

 

[PAUL BAAS]

alright......... thats what i thought.......cmos has probably fanout around 40 gates.........thanks friend