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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......
 

Hi,

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

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

Klaus
 

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
 

Hi,

Susan is right, your description is confusing.

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

Klaus
 

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,
 

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.
 

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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