Hello,

I’m trying to use PIC16F628A to control 2 pcs of 74AHCT595 (Texas instrument) shift registers for matrix display.

In the data sheets for both parts, max frequency for the MCU is 20Mhz, but the shift register min required 85Mhz!

Would someone point me the right way of selecting the correct frequency? Thanks for your time.

 

Hello,

I’m trying to use PIC16F628A to control 2 pcs of 74AHCT595 (Texas instrument) shift registers for matrix display.

In the data sheets for both parts, max frequency for the MCU is 20Mhz, but the shift register min required 85Mhz!

Would someone point me the right way of selecting the correct frequency? Thanks for your time.

Hahaha. That's a funny idea they need at least 85 MHz.

You can indeed apply pulses manually.

 

...but the shift register min required 85Mhz!

Not 85 MHz minimum... 85 MHz MAXIMUM.

One pulse per day is acceptable.

 

Page 7, fmax is at least 85MHz, this means it will work up to 85MHz or maybe higher, not that the minimum operating frequnecy is 85MHz.