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PSoC 1 External Clock | Cypress Semiconductor

PSoC 1 External Clock

Summary: 2 Replies, Latest post by Pushek Madaan on 17 Feb 2011 12:03 PM PST
Verified Answers: 0
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Grandad's picture
1 post

I wish to feed an externally-generated 32.768 KHz clock signal into the XTALin pin (P1[1]) of an 8-pin PSOC 1 device, and use this to synchronise the PLL.  Since the XTALout pin (P1[0]) will not be needed, can I use this pin for general purpose I/O ?


graa's picture
Cypress Employee
223 posts

I dont think this is possible.  When the ECO is enabled, the oscillator circuit gets connected to P1[0] and P1[1].  So, even if you are not using the XTALOUT pin to drive a crystal, this pin can not be controlled independently through PRT1DR register or by the Global bus as there will be a contention with the ECO circuit.

Best Regards,

pmad's picture
Cypress Employee
100 posts

 This is not possible because whenever you connect a crystal and enable the same, then the internal circuit which is generally a inverter complements the line and output it to XTALOUT line. Thus, even though you are not connecting using the XTALOUT for ECO purpose but you won't be able to use for any GPIO purpose becaus einternal circuitry drives this line.


Best regards,


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