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???
02/16/05 13:52
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#87646 - wire wrap and breadboards
Responding to: ???'s previous message
Wire wrap and breadboards severely limit what you can use of modern chips. It is a common misconception that it is the clock speed that has to be watched - WRONG, it is the risetimes and the power. I am not looking at a datasheet, so the numbers are approximate from memory:
a 74ALS raise 40mA in 2ns
a 74HC rasie 1 mA in 10ns
you figure.

Also when breadboarding/wirewrapping do not use processors with a Max clock speed above 12 MHX YES a max speed - again the clock does not matter but the max speed indicates the risetimes of the chip.

NOW here is a problem: the chips are specified as capable of a max speed of .. NOTHING forbid a mnufacturere from substituting a faster chip and label it the same (NOTE there are never any minimum rise times listed) so you may do everything right (supposedly slow uC, supposedly slow chips) and still get in trouble with your breadboard/wire wrap.

My suggestion:
Buy a 'protoboard" all will be well and you can tap the port signals off the protoboard to your breadboard (if needed round the pulses with some small RC circuits).

Erik

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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