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???
02/16/05 15:01
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#87660 - LS, HCT and maybe AHCT
Responding to: ???'s previous message
Christian said:
Which i could use in a breadboard without suffering big problems like Kai said, i'm very concerned about this.

SN74LS08, SN74HCT08 and maybe SN74AHCT08 should work.

Of course, very much depends on your actual design, how you manage the ground routing, how much current is driven by the fast digital chips and how properly power supply decoupling is done.

It cannot be guaranteed, that the one will work and the other not. But it should be clear, that the faster the chip is the more demanding the use of solid ground plane is. This solid ground plane provides not only lowest possible inductivity for the power supply decoupling measures, but also provides a low inductivity ground return path for the output signals of such a fast chip.

With breadboard or wirewrap you add an enormous extra portion of inductivity to each line, which per se puts trouble into your design. But whether this actually results in a disaster or not depends on your actual circuit.

One trick: If you have no solid ground plane for the ground return current of each decoupling capacitor, then connect two or three totally individual 10...100nF decoupling capacitors with shortest connections to the power supply pins of each chip. This will enormously decrease effective inductivity of power supply decoupling, because now three capacitors are connected in parallel. By this you can decrease noise across power supply pins by about a factor of two! This can directly be observed by the help of a good scope, by the way.
Of course, you will not result in a performance that is better than using a solid ground plane...


Kai

List of 37 messages in thread
TopicAuthorDate
Problem getting 8051 chip to work            01/01/70 00:00      
   tie ~EA pin to Vcc            01/01/70 00:00      
      tie Vpp/~EA pin to Vcc            01/01/70 00:00      
         to connect or not?            01/01/70 00:00      
            conbnect            01/01/70 00:00      
            If it helps....            01/01/70 00:00      
               Reset Capacitor            01/01/70 00:00      
            connect            01/01/70 00:00      
      T89C51RD2            01/01/70 00:00      
         This device is ISP            01/01/70 00:00      
   VCC and GND?            01/01/70 00:00      
   I think you do not load            01/01/70 00:00      
   Series resistor for LED?            01/01/70 00:00      
      74F14            01/01/70 00:00      
         give me +1 too            01/01/70 00:00      
            done            01/01/70 00:00      
      Sorry            01/01/70 00:00      
         LED Polarity            01/01/70 00:00      
            Does not seem to be the cause            01/01/70 00:00      
   Ouch!            01/01/70 00:00      
      FAST-TTL and breadboarded design            01/01/70 00:00      
         Ground bounce            01/01/70 00:00      
            Bad news 74F =(            01/01/70 00:00      
               HCT?            01/01/70 00:00      
                  LS, HCT and maybe AHCT            01/01/70 00:00      
            Got it            01/01/70 00:00      
               wire wrap and breadboards            01/01/70 00:00      
                  I use protoboard            01/01/70 00:00      
                     the problem with that is            01/01/70 00:00      
                        Thanks            01/01/70 00:00      
                     Why do you want to use 74F chips?            01/01/70 00:00      
                        well...            01/01/70 00:00      
   maybe you are still in ISP mode?            01/01/70 00:00      
   1st things 1st please            01/01/70 00:00      
   Thanks            01/01/70 00:00      
      bounce on non PCB            01/01/70 00:00      
   Analytical thinking            01/01/70 00:00      

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