Email: Password: Remember Me | Create Account (Free)

Back to Subject List

Old thread has been locked -- no new posts accepted in this thread
???
07/09/04 17:59
Read: times


 
#73898 - RE: ALE with 33pF capacitor works ????
Responding to: ???'s previous message
Sjoerd wrote:

I have made a single layer PCB with on it a Dallas DS80C320, ADconverter , 2 serial ports, I2C and so on.I use XDATA. P0 and P2 are used for XDATA with 27512, 48T08 and 74HCT373. I tested the program with a PICE-51 In Circuit Emulator. When i put the program in the 27512, it did not work, till i put a probe from an oscilloscope on the ALE-pin. I put a capacitor of 33 pF on pin 11 (is connected to the ALE-pin of the procesor) of the 74HCT373 and all is working fine. I think this is not normal. What did i wrong?

Peter answered:

You must use 74HC373 or 74AC373 to do the trick. The HCT was to sensitive against noise.

I'm sorry, but to use a ACMOS part to fix a ground bounce problem is not at all a good idea!
This ALE stuff is discussed here:

http://korea.maxim-ic.com/appnotes....number/551

Means, the noise superimposed on ALE line comes from too high capacitive loading OR from not adequate ground routing! And if Sjoerd tells, that is has made a SINGLE LAYER PCB, then we should recommend him to make a DOUBLE SIDED PCB containing a solid ground plane and not to use an ACMOS chip, which produces the dirtiest noise one can imagine, especially if only a single sided board is used...

Sjoerd, you have decided to drive a Ferrari with wooden wheels! If you want to run such a nice and fast chip like DS80C320, then use the proper PCB stuff for it.

Kai

List of 5 messages in thread
TopicAuthorDate
ALE with 33pF capacitor works ????            01/01/70 00:00      
   RE: ALE with 33pF capacitor works ????            01/01/70 00:00      
      RE: ALE with 33pF capacitor works ????            01/01/70 00:00      
         RE: ALE with 33pF capacitor works ????            01/01/70 00:00      
            RE: ALE with 33pF capacitor works ????            01/01/70 00:00      

Back to Subject List