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Text replacement - " (archived) by Ken Stone, 2004, with permission of the author" to " by Ken Stone, 2004, with permission of the author - archived"
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'''CGS54''' the '''CGS XOR/XNOR logic''' board is an add-on for the [[CGS pulse divider and
== A little on how it works ==
[[File:cgs_schem_cgs54v11_xor.gif|thumb|center|465px|The schematic of the XOR/XNOR Logic VER1.1]]
Normally the two inputs of each op-amp are held (approximately) 1.2 volts apart via the pull-up and pull-down resistors, and the four diodes in the input circuit. Connecting two similar input voltages to the inputs will not affect this
Once the two input voltages begin to differ, the diode connected between the pull-up resistor and the lower of the two input voltages will pull the connected comparator inputs down, while the diode connected to the pull-down resistor and the higher of the two input voltages will pull the connected comparator inputs up. The other diodes will cease to conduct.
Once the two input are taken more than 1.2 volts apart, the voltage at the diode- pull-up resistor junction will be lower than that at the diode- pull-down resistor, and the relationship between the comparator inputs will be reversed, i.e. on the XOR, the inverting input will be lower than the non-inverting input, resulting in the op-amp output being positive, and the opposite
Technically there is a tiny band where the difference between the two inputs can result in an "analog" (i.e. not logic 1, or logic 0) voltage at the output, though this may only be an issue if using the gates with analog input voltages.
The outputs of the op-amp comparators are passed
The LEDs indicate the output levels of the gates. As the gates share a common input structure, these LED have a complimentary relationship - if one is lit, the other is off. As such, a single LED would suffice to indicate the state of both gates.
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When inserting ICs into sockets, take care not to accidentally bend any of the pins under the chip. Also, make sure the notch on the chip is aligned with the notch marked on the PCB overlay.
{| class="wikitable"
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| LN||to anode of XNOR LED
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* Substitute 1k5 for the two 1k8 resistors if running from +/-12 volts.
* PCB is 1" x 2" with two 3mm mounting holes 0.15" in from the bottom and edges. It is designed to sit above one end of a regular 2" width CGS PCB.
== CC-BY-NC ==
Readers are permitted to construct these circuits for their own personal use only. Ken Stone retains all rights to his work.
== See also ==
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== References ==
* [https://web.archive.org/web/
== External links ==
* [http://groups.yahoo.com/group/cgs_synth CGS Synth discussion group], for discussion of locating parts, modifications and corrections etc.
* [http://bompiler.com/pcb/cgs54 CGS54 BOM] at BOMpiler
=== Suppliers ===
* [http://www.elby-designs.com/webtek/cgs/cgs54/cgs54_xor.html CGS54 XOR/NXOR Logic], revision 1.1, Elby Designs
[[Category:CGS
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