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Why is this clock signal connected to a capacitor to gnd?


Is it possible to provide power using (effectively) a single wire?Capacitor negative voltage in flip flop circuitexactly why does a capacitor build up charge when hooked up to a battery?Help me understand capacitor dischargingWhy can't we read voltage between just one pin of a loaded capacitor and any ground?Modelling a capacitor whose dielectric has resistance as a circuit elementThe voltage between the plates of a capacitorHow does this capacitor operate in this circuit?Can this circuit work as an UHF oscillator?Capacitor as Noise removal (Theoratical)?













1












$begingroup$


I am trying to understand the following circuit:



enter image description here



My problem is to understand why the CLK signal is connected to the capacitor (C7). The bottom side of C7 is connected with a resistor to GND. This means that the "plate" will (after some delay) have the same potential as GND. The upper "plate" will oscillate with the CLK signal.
The logic is connected to the bottom side, so I don't understand how the NAND Gate can ever get some other input than LOW on the bottom pin. This means that the NAND gate will never output LOW and thus the RAM never stores anything, which doesn't make sense.



The only effect the capacitor could have in my understanding is to delay and flatten changes in the clock signal, but I don't understand the use of this.



Also I don't understand the meaning of the resistor. It pushes the loading time of the capacitor, but after the bottom side is on GND potential there will be no current after that.



I hope someone can help me understand this.










share|improve this question











$endgroup$











  • $begingroup$
    This is a large schematic and is hard to read due to the scaling. Could you perhaps add an arrow or circle to show what capacitor you mean?
    $endgroup$
    – Hearth
    2 hours ago











  • $begingroup$
    Can you show where the CLK signal originates?
    $endgroup$
    – vini_i
    2 hours ago










  • $begingroup$
    @Hearth... Click on the schematic for a larger version.
    $endgroup$
    – BobT
    2 hours ago










  • $begingroup$
    Since the clock is oscillating, why do you believe the bottom plate of capacitor is at steady state?
    $endgroup$
    – crasic
    2 hours ago










  • $begingroup$
    @crasic: Yeah I just realized it is an alternating voltage so it is an impedance rather than a real capacity.
    $endgroup$
    – birdfreeyahoo
    1 hour ago















1












$begingroup$


I am trying to understand the following circuit:



enter image description here



My problem is to understand why the CLK signal is connected to the capacitor (C7). The bottom side of C7 is connected with a resistor to GND. This means that the "plate" will (after some delay) have the same potential as GND. The upper "plate" will oscillate with the CLK signal.
The logic is connected to the bottom side, so I don't understand how the NAND Gate can ever get some other input than LOW on the bottom pin. This means that the NAND gate will never output LOW and thus the RAM never stores anything, which doesn't make sense.



The only effect the capacitor could have in my understanding is to delay and flatten changes in the clock signal, but I don't understand the use of this.



Also I don't understand the meaning of the resistor. It pushes the loading time of the capacitor, but after the bottom side is on GND potential there will be no current after that.



I hope someone can help me understand this.










share|improve this question











$endgroup$











  • $begingroup$
    This is a large schematic and is hard to read due to the scaling. Could you perhaps add an arrow or circle to show what capacitor you mean?
    $endgroup$
    – Hearth
    2 hours ago











  • $begingroup$
    Can you show where the CLK signal originates?
    $endgroup$
    – vini_i
    2 hours ago










  • $begingroup$
    @Hearth... Click on the schematic for a larger version.
    $endgroup$
    – BobT
    2 hours ago










  • $begingroup$
    Since the clock is oscillating, why do you believe the bottom plate of capacitor is at steady state?
    $endgroup$
    – crasic
    2 hours ago










  • $begingroup$
    @crasic: Yeah I just realized it is an alternating voltage so it is an impedance rather than a real capacity.
    $endgroup$
    – birdfreeyahoo
    1 hour ago













1












1








1





$begingroup$


I am trying to understand the following circuit:



enter image description here



My problem is to understand why the CLK signal is connected to the capacitor (C7). The bottom side of C7 is connected with a resistor to GND. This means that the "plate" will (after some delay) have the same potential as GND. The upper "plate" will oscillate with the CLK signal.
The logic is connected to the bottom side, so I don't understand how the NAND Gate can ever get some other input than LOW on the bottom pin. This means that the NAND gate will never output LOW and thus the RAM never stores anything, which doesn't make sense.



The only effect the capacitor could have in my understanding is to delay and flatten changes in the clock signal, but I don't understand the use of this.



Also I don't understand the meaning of the resistor. It pushes the loading time of the capacitor, but after the bottom side is on GND potential there will be no current after that.



I hope someone can help me understand this.










share|improve this question











$endgroup$




I am trying to understand the following circuit:



enter image description here



My problem is to understand why the CLK signal is connected to the capacitor (C7). The bottom side of C7 is connected with a resistor to GND. This means that the "plate" will (after some delay) have the same potential as GND. The upper "plate" will oscillate with the CLK signal.
The logic is connected to the bottom side, so I don't understand how the NAND Gate can ever get some other input than LOW on the bottom pin. This means that the NAND gate will never output LOW and thus the RAM never stores anything, which doesn't make sense.



The only effect the capacitor could have in my understanding is to delay and flatten changes in the clock signal, but I don't understand the use of this.



Also I don't understand the meaning of the resistor. It pushes the loading time of the capacitor, but after the bottom side is on GND potential there will be no current after that.



I hope someone can help me understand this.







capacitor clock ram






share|improve this question















share|improve this question













share|improve this question




share|improve this question








edited 2 hours ago









laptop2d

27.2k123584




27.2k123584










asked 2 hours ago









birdfreeyahoobirdfreeyahoo

1153




1153











  • $begingroup$
    This is a large schematic and is hard to read due to the scaling. Could you perhaps add an arrow or circle to show what capacitor you mean?
    $endgroup$
    – Hearth
    2 hours ago











  • $begingroup$
    Can you show where the CLK signal originates?
    $endgroup$
    – vini_i
    2 hours ago










  • $begingroup$
    @Hearth... Click on the schematic for a larger version.
    $endgroup$
    – BobT
    2 hours ago










  • $begingroup$
    Since the clock is oscillating, why do you believe the bottom plate of capacitor is at steady state?
    $endgroup$
    – crasic
    2 hours ago










  • $begingroup$
    @crasic: Yeah I just realized it is an alternating voltage so it is an impedance rather than a real capacity.
    $endgroup$
    – birdfreeyahoo
    1 hour ago
















  • $begingroup$
    This is a large schematic and is hard to read due to the scaling. Could you perhaps add an arrow or circle to show what capacitor you mean?
    $endgroup$
    – Hearth
    2 hours ago











  • $begingroup$
    Can you show where the CLK signal originates?
    $endgroup$
    – vini_i
    2 hours ago










  • $begingroup$
    @Hearth... Click on the schematic for a larger version.
    $endgroup$
    – BobT
    2 hours ago










  • $begingroup$
    Since the clock is oscillating, why do you believe the bottom plate of capacitor is at steady state?
    $endgroup$
    – crasic
    2 hours ago










  • $begingroup$
    @crasic: Yeah I just realized it is an alternating voltage so it is an impedance rather than a real capacity.
    $endgroup$
    – birdfreeyahoo
    1 hour ago















$begingroup$
This is a large schematic and is hard to read due to the scaling. Could you perhaps add an arrow or circle to show what capacitor you mean?
$endgroup$
– Hearth
2 hours ago





$begingroup$
This is a large schematic and is hard to read due to the scaling. Could you perhaps add an arrow or circle to show what capacitor you mean?
$endgroup$
– Hearth
2 hours ago













$begingroup$
Can you show where the CLK signal originates?
$endgroup$
– vini_i
2 hours ago




$begingroup$
Can you show where the CLK signal originates?
$endgroup$
– vini_i
2 hours ago












$begingroup$
@Hearth... Click on the schematic for a larger version.
$endgroup$
– BobT
2 hours ago




$begingroup$
@Hearth... Click on the schematic for a larger version.
$endgroup$
– BobT
2 hours ago












$begingroup$
Since the clock is oscillating, why do you believe the bottom plate of capacitor is at steady state?
$endgroup$
– crasic
2 hours ago




$begingroup$
Since the clock is oscillating, why do you believe the bottom plate of capacitor is at steady state?
$endgroup$
– crasic
2 hours ago












$begingroup$
@crasic: Yeah I just realized it is an alternating voltage so it is an impedance rather than a real capacity.
$endgroup$
– birdfreeyahoo
1 hour ago




$begingroup$
@crasic: Yeah I just realized it is an alternating voltage so it is an impedance rather than a real capacity.
$endgroup$
– birdfreeyahoo
1 hour ago










3 Answers
3






active

oldest

votes


















1












$begingroup$

C7 and R58 form a high pass filter, also known as a differentiator.



The purpose of using a differentiator in this spot is to cause a short pulse on the rising and falling edge of the clock signal.



This diagram shows the effect of a differentiator on a square wave (which your clock will be.)



enter image description here



As you can see, it makes short pulses on the edges of the square wave.




I'm not sure why that circuit needs the short pulses instead of the square wave, though. Too many ICs I'd have to look up to figure out what is going on.






share|improve this answer









$endgroup$




















    2












    $begingroup$

    The circuit overall is a 16-byte memory bank for a homebrew computer of some sort, with manual programming capability via the switches and lights. Probably the most complicated 16 bytes of memory you'll ever see!



    The R-C combination being asked about is used only when the CPU is running — i.e., when PROG is not asserted. It is probably being used to shorten the high time of the write-enable pulses going to the memory chips in order to meet hold-time requirements when the CPU is writing to memory. This only works if the clock high time is significantly longer than the R-C time constant.



    10 nF × 1 kΩ = 10 µs



    So presumably the clock is something less than 50 kHz.



    Actually, the 74189 is not a slow part — the minimum write pulse width is a few tens of ns — so the R-C time constant could be much shorter, by a couple of orders of magnitude.






    share|improve this answer











    $endgroup$




















      1












      $begingroup$

      That is a high pass RC filter with a pole at 15.9kHz, which is unusual for a clock signal because it will attenuate the signal somewhat. The purpose is possibly to keep the clock more than 15-20kHz, to keep the memory running above that speed as a lower clock speed would not transition.






      share|improve this answer









      $endgroup$













        Your Answer





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        3 Answers
        3






        active

        oldest

        votes








        3 Answers
        3






        active

        oldest

        votes









        active

        oldest

        votes






        active

        oldest

        votes









        1












        $begingroup$

        C7 and R58 form a high pass filter, also known as a differentiator.



        The purpose of using a differentiator in this spot is to cause a short pulse on the rising and falling edge of the clock signal.



        This diagram shows the effect of a differentiator on a square wave (which your clock will be.)



        enter image description here



        As you can see, it makes short pulses on the edges of the square wave.




        I'm not sure why that circuit needs the short pulses instead of the square wave, though. Too many ICs I'd have to look up to figure out what is going on.






        share|improve this answer









        $endgroup$

















          1












          $begingroup$

          C7 and R58 form a high pass filter, also known as a differentiator.



          The purpose of using a differentiator in this spot is to cause a short pulse on the rising and falling edge of the clock signal.



          This diagram shows the effect of a differentiator on a square wave (which your clock will be.)



          enter image description here



          As you can see, it makes short pulses on the edges of the square wave.




          I'm not sure why that circuit needs the short pulses instead of the square wave, though. Too many ICs I'd have to look up to figure out what is going on.






          share|improve this answer









          $endgroup$















            1












            1








            1





            $begingroup$

            C7 and R58 form a high pass filter, also known as a differentiator.



            The purpose of using a differentiator in this spot is to cause a short pulse on the rising and falling edge of the clock signal.



            This diagram shows the effect of a differentiator on a square wave (which your clock will be.)



            enter image description here



            As you can see, it makes short pulses on the edges of the square wave.




            I'm not sure why that circuit needs the short pulses instead of the square wave, though. Too many ICs I'd have to look up to figure out what is going on.






            share|improve this answer









            $endgroup$



            C7 and R58 form a high pass filter, also known as a differentiator.



            The purpose of using a differentiator in this spot is to cause a short pulse on the rising and falling edge of the clock signal.



            This diagram shows the effect of a differentiator on a square wave (which your clock will be.)



            enter image description here



            As you can see, it makes short pulses on the edges of the square wave.




            I'm not sure why that circuit needs the short pulses instead of the square wave, though. Too many ICs I'd have to look up to figure out what is going on.







            share|improve this answer












            share|improve this answer



            share|improve this answer










            answered 2 hours ago









            JREJRE

            23.1k54075




            23.1k54075























                2












                $begingroup$

                The circuit overall is a 16-byte memory bank for a homebrew computer of some sort, with manual programming capability via the switches and lights. Probably the most complicated 16 bytes of memory you'll ever see!



                The R-C combination being asked about is used only when the CPU is running — i.e., when PROG is not asserted. It is probably being used to shorten the high time of the write-enable pulses going to the memory chips in order to meet hold-time requirements when the CPU is writing to memory. This only works if the clock high time is significantly longer than the R-C time constant.



                10 nF × 1 kΩ = 10 µs



                So presumably the clock is something less than 50 kHz.



                Actually, the 74189 is not a slow part — the minimum write pulse width is a few tens of ns — so the R-C time constant could be much shorter, by a couple of orders of magnitude.






                share|improve this answer











                $endgroup$

















                  2












                  $begingroup$

                  The circuit overall is a 16-byte memory bank for a homebrew computer of some sort, with manual programming capability via the switches and lights. Probably the most complicated 16 bytes of memory you'll ever see!



                  The R-C combination being asked about is used only when the CPU is running — i.e., when PROG is not asserted. It is probably being used to shorten the high time of the write-enable pulses going to the memory chips in order to meet hold-time requirements when the CPU is writing to memory. This only works if the clock high time is significantly longer than the R-C time constant.



                  10 nF × 1 kΩ = 10 µs



                  So presumably the clock is something less than 50 kHz.



                  Actually, the 74189 is not a slow part — the minimum write pulse width is a few tens of ns — so the R-C time constant could be much shorter, by a couple of orders of magnitude.






                  share|improve this answer











                  $endgroup$















                    2












                    2








                    2





                    $begingroup$

                    The circuit overall is a 16-byte memory bank for a homebrew computer of some sort, with manual programming capability via the switches and lights. Probably the most complicated 16 bytes of memory you'll ever see!



                    The R-C combination being asked about is used only when the CPU is running — i.e., when PROG is not asserted. It is probably being used to shorten the high time of the write-enable pulses going to the memory chips in order to meet hold-time requirements when the CPU is writing to memory. This only works if the clock high time is significantly longer than the R-C time constant.



                    10 nF × 1 kΩ = 10 µs



                    So presumably the clock is something less than 50 kHz.



                    Actually, the 74189 is not a slow part — the minimum write pulse width is a few tens of ns — so the R-C time constant could be much shorter, by a couple of orders of magnitude.






                    share|improve this answer











                    $endgroup$



                    The circuit overall is a 16-byte memory bank for a homebrew computer of some sort, with manual programming capability via the switches and lights. Probably the most complicated 16 bytes of memory you'll ever see!



                    The R-C combination being asked about is used only when the CPU is running — i.e., when PROG is not asserted. It is probably being used to shorten the high time of the write-enable pulses going to the memory chips in order to meet hold-time requirements when the CPU is writing to memory. This only works if the clock high time is significantly longer than the R-C time constant.



                    10 nF × 1 kΩ = 10 µs



                    So presumably the clock is something less than 50 kHz.



                    Actually, the 74189 is not a slow part — the minimum write pulse width is a few tens of ns — so the R-C time constant could be much shorter, by a couple of orders of magnitude.







                    share|improve this answer














                    share|improve this answer



                    share|improve this answer








                    edited 1 hour ago

























                    answered 1 hour ago









                    Dave TweedDave Tweed

                    123k9152265




                    123k9152265





















                        1












                        $begingroup$

                        That is a high pass RC filter with a pole at 15.9kHz, which is unusual for a clock signal because it will attenuate the signal somewhat. The purpose is possibly to keep the clock more than 15-20kHz, to keep the memory running above that speed as a lower clock speed would not transition.






                        share|improve this answer









                        $endgroup$

















                          1












                          $begingroup$

                          That is a high pass RC filter with a pole at 15.9kHz, which is unusual for a clock signal because it will attenuate the signal somewhat. The purpose is possibly to keep the clock more than 15-20kHz, to keep the memory running above that speed as a lower clock speed would not transition.






                          share|improve this answer









                          $endgroup$















                            1












                            1








                            1





                            $begingroup$

                            That is a high pass RC filter with a pole at 15.9kHz, which is unusual for a clock signal because it will attenuate the signal somewhat. The purpose is possibly to keep the clock more than 15-20kHz, to keep the memory running above that speed as a lower clock speed would not transition.






                            share|improve this answer









                            $endgroup$



                            That is a high pass RC filter with a pole at 15.9kHz, which is unusual for a clock signal because it will attenuate the signal somewhat. The purpose is possibly to keep the clock more than 15-20kHz, to keep the memory running above that speed as a lower clock speed would not transition.







                            share|improve this answer












                            share|improve this answer



                            share|improve this answer










                            answered 2 hours ago









                            laptop2dlaptop2d

                            27.2k123584




                            27.2k123584



























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