Pull-up register for bus interface in 8051

[pawan yadav]

do we need to connect pullup registor in port0, while using it as address and data lines for external ram

 

[CMOS]

pull up 8052

No you dont need pull-up for bus interface.

 

[jjohn]

8051

Yes you require..

 

[svicent]

Re: 8051

The pull-up resistor is absent on Port0, except when functioning as the external address/data bus, so you dont need pull-up resistor when using it as address and data lines for external ram.

 

[vignesh_baliga]

Re: 8051

If I remember correctly the diagram shown in 8051 book by K J Ayala, Port 0 does not have internal pull-up, whereas other ports have. Since you are planning to interface RAM, you will also need a Latch, So the Port0 pins will have to drive 2 loads. I suggest using a weak pull-ups, may be 33K !?
- Vignesh

 

[ivar4ever]

Re: 8051

port 0 does nt have internal pull up so it do require an external pullup resister.

 

[CMOS]

Re: 8051

Check out this diagram, Port-0 doesnt require pull-ups if used as external data/address bus. The external devices like RAM, EPROM have internal pull-up which are enabled when OE\ pins is set low. Any external pull-up on port-0 may cause bus-contention since RAM/EPROM cannot sink fair amount of current to make a pin low.

I've use such configuration many times without any pull-ups.

Check this->
https://www.pjrc.com/tech/8051/dev-board-schematic.html

 

[xischaune]

Re: 8051

Yes you need it

 

[bauer]

8051

I would suggest to put, no harm .....

 

[sanjiv]

Re: 8051

Port 0 has two fold role: if external memory is used, it contains the lower address byte (addresses A0-A7), otherwise all bits of the port are either input or output. Another feature of this port comes to play when it has been designated as output. Unlike other ports, Port 0 lacks the "pull up" resistor (resistor with +5V on one end). This seemingly insignificant change has the following consequences:

When designated as input, pin of Port 0 acts as high impedance offering the infinite input resistance with no "inner" voltage.

When designated as output, pin acts as "open drain". Clearing a port bit grounds the appropriate pin on the case (0V). Setting a port bit makes the pin act as high impedance. Therefore, to get positive logic (5V) at output, external "pull up" resistor needs to be added for connecting the pin to the positive pole.

Therefore, to get one (5V) on the output, external "pull up" resistor needs to be added for connecting the pin to the positive pole.

 

[vignesh_baliga]

Re: 8051

Well, Now after reading the forum posting at 8052.com, I can’t say You “need” to have Pull-ups.
Pls. have a look at this
**broken link removed**
This post was specific to AT89S8252, and Mr. Ijaz indicates that it has internal pull-ups, and pls. read the datasheet.
- Vignesh

 

[rosarioantony]

Re: 8051

u dont need pull up. open collector part will be used only when port 0 pins are used as output .

Added after 7 minutes:

the text below is taken from atmel's AT89C51 hardware mamual..and it is clearly mentioned u dont need any pullups...fin

In any case, the low byte of the address is time-multiplexed with the data byte on Port 0.
The ADDR/DATA signal drives both FETs in the Port 0 output buffers. Thus, in this
application the Port 0 pins are not open-drain outputs, and do not require external pullups.
Signal ALE (address latch enable) should be used to capture the address byte into
an external latch. The address byte is valid at the negative transitions of ALE. Then, in a
write cycle, the data byte to be written appears on Port 0 just before WR is activated, and
remains there until after WR is deactivated. In a read cycle, the incoming byte is accepted at
Port 0 just before the read strobe is deactivated.

 

[smith_suez]

Re: 8051

You can add .no harm

 

[shabazmondal]

Re: 8051

Check out this diagram, Port-0 doesnt require pull-ups if used as external data/address bus. The external devices like RAM, EPROM have internal pull-up which are enabled when OE\ pins is set low. Any external pull-up on port-0 may cause bus-contention since RAM/EPROM cannot sink fair amount of current to make a pin low.

I've use such configuration many times without any pull-ups.

Check this->
8051 Development Board Design

Please guys,stop this ambiguity on this thread.
As 'CMOS' says, it does not require a pull up when connected to external RAM or EPROM.
This is correct and final.
Read the link before you post.

 

[ckshivaram]

what made you open this 5 years old thread and tell others to stop this thread???

 

[shabazmondal]

what made you open this 5 years old thread and tell others to stop this thread???

I had started a thread with a querry,wherein i was directed to this thread,this solved my querry though it did did confuse me with the ambiguity of the replies on the thread.So i thought its better to stop the ambiguity and not the thread, so that it can be referred in future by the users.Thats it.