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'[PIC]: 16F877 usart - local echo??'
2000\12\18@124042 by John Walshe

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Hi,
I've been working with a PIC16F877 today primarily with the usart(sci) port
and have come up against what appears to be a local echo within the IC.
Whatever I transmit immediately appears at the rx pin ( I have even lifted
the RX leg to make sure that there is not a short causing this).
Is this to be expected with this device - I certainly could not see anything
in the specs.
Best regards,
John

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2000\12\18@150910 by Wynn Rostek

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> Whatever I transmit immediately appears at the rx pin

John,

I've had a 16F877 designed into a product for about 6 weeks now and have
never seen this.

Wynn Rostek

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2000\12\18@180457 by Olin Lathrop

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> I've been working with a PIC16F877 today primarily with the usart(sci)
port
> and have come up against what appears to be a local echo within the IC.
> Whatever I transmit immediately appears at the rx pin ( I have even lifted
> the RX leg to make sure that there is not a short causing this).
> Is this to be expected with this device - I certainly could not see
anything
> in the specs.

The USART in normal asynchronous mode definitely does not do this.  I've
used it many times, and such an echo would have messed quite a few projects.
However, I don't understand exactly what you mean by "usart(sci)".


*****************************************************************
Olin Lathrop, embedded systems consultant in Devens Massachusetts
(978) 772-3129, spam_OUTolinTakeThisOuTspamembedinc.com, http://www.embedinc.com

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2000\12\19@065657 by Andrew Kunz

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>However, I don't understand exactly what you mean by "usart(sci)".

Means he graduated from Mot to Microchip.

Andy

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2000\12\19@072020 by John Walshe

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Actually I was just reflecting what Microchip called the port in their
literature but to be clear I am using said port in it's Asynchronous mode. I
still have the problem and it's definitely in the chip (both of them - I
have two!), but I've put in a workaround by not switching on the RX logic
until I want it and when I do I clear out the FIFO (2 deep buffer) before
accepting any data.
I have a DIP '877 somewhere at home which I'll try also. I'm using the
Hitech SCI (oops theres theat word again)code sample which works admirably
for me on other devices. I've checked this and it all appears ok.

If I figure out the cause I'll let you know

John

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