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jawaria
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Join Date: Jul 2013
Posts: 2

Electronics (Microcontroller)

11/08/2014 12:23 PM

Why in micro controller 8051 ((ATMEGA89C51) pull up resistors are not connected internally at port 0? While there are internally built resistors to other ports?
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redfred
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Engineering Fields - Electrical Engineering - Been there, done that. Engineering Fields - Control Engineering - New Member

Join Date: Dec 2008
Location: Long Island NY
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#1

Re: Electronics (Microcontroller)

11/08/2014 4:11 PM

I believe you will find your answer by looking at how a zero becomes a one on port 0.

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lewisthebear
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#2

Re: Electronics (Microcontroller)

11/09/2014 10:41 PM

Port 0 is an 8-bit open-drain bi-directional I/O port. As an output port, each pin can sink eight TTL inputs. When 1s are written to port 0 pins, the pins can be used as high- impedance inputs.

Port 0 may also be configured to be the multiplexed low-order address/data bus during accesses to external program and data memory. In this mode P0 has internal pullups.

Port 0 also receives the code bytes during Flash programming, and outputs the code bytes during program verification. External pullups are required during program verification.

Atmel Datasheet

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