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[PIC] 2 MAX232, HCF4066 & PIC microcontrollers

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mmbabar41

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Hi friends, I am using 2 MAX232, HCF4066 & PIC microcontrollers. I want to make communication of dial guage with PIC.
I have made connections for dial guage as given in image:
I tested dial guage by connecting to the PC through serial cable then dial guage is responds. Now I am able to transmit signal by enabling control pin of 4066 but not getting any response from dial guage. I am attaching the circuit diagram here. Please help me......
 

KlausST

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Hi,

Please use the "insert image" button. insertImage.PNG

***
Mind to pullup unused TxD (idle high)

Klaus
 

Aussie Susan

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I'm struggling to understand which signal you are having problems with. You have listed a number of different lines in the image but I can't work out which one has the "...response from dial guage[sic]...". Perhaps if you use the names as they are on the diagram it would help.
However I would suggest that you use a scope to trace the signal to see where it stops. Then you can again tell us what works and what doesn't using the labels from your diagram.
Susan
 

KlausST

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Hi,

Susan is right, your description is confusing.

Mind to pullup unused TxD (idle high)
Ican't find the pullups.

Klaus
 

FvM

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As far as I see, muxing the PIC UART between "Digital Dial" and "PC" RS-232 interfaces should work. I agree that the schematic could be better readable.

But the DB-9 pins assignment isn't standard RS-232, e.g. you have TxD at pin 4. As long we don't know the "dial gauge" interface operation, we can't guess what's the problem.

MAX232 has already internal weak pull-ups at /TXIN as far as I know,
 

spudboy488

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Pin 4 is DTR and it might be used as a control/trigger to the "dial". It also looks like the communication is inbound (from the dial to the PIC) only. The pull-up to keep TX idle high (which it should be) is on U10, Pin 10.
 

KlausST

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Hi,

With my expression "unused TxD" I meant "deselected TxD" = switched OFF

I read the datasheet. The pullup is about 400k. For unconnected pins this might be ok. But it is too weak for a signal that is wired to a CMOS switch.

Klaus
 

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