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PIC nid extent port!


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jovenlim89

Wed Sep 02 2009, 07:23PM

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HI.. I m using PIC16F877A..
But I nid more port for my project..I was suggest that using shift register and latch..But I dunno how to do it? Can any1 send me the circuit pls...:-|

Hope u all can help me~Thx..

Chiru

Wed Sep 02 2009, 08:55PM

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One way of extending port is by using the 82C55. Download datasheet for detailed information, keep in mind the speed limit. Ofcourse you need to write a code for the interface.:bye

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jovenlim89

jovenlim89

Wed Sep 02 2009, 09:06PM

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Thx so much... The code that I need to write is at PIC or the chip u mention js now? Hope can get more tips from u..

Hope u all can help me~Thx..

ExperimenterUK

Thu Sep 03 2009, 09:04AM

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Given the cost of chips these days I would consider adding another PIC as a slave.

Use a high speed serial link to read and update the ports on the slave PIC.
How many more ports do you need ?

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jovenlim89

jovenlim89

Sat Sep 05 2009, 02:40AM

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lolx..Thanks...I m oso thinking of it... I need about 39 port for my project..Do you think adding another PIC is the best way? And what do u mean by use a high speed serial link?

Hope u all can help me~Thx..

Ajay Bhargav

Sat Sep 05 2009, 04:10AM

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high speed serial link means, serial communication over higher speed/data rate. you ca use either uart on higher baud or SPI at higher data rate.

using extra controller is good, but you should also make sure it matches your project requirement. the shift register latch (CD4094) is commonly used for port expanding coz it need only 3 pins to make an 8 bit port. and no extra pins needed if you want to go further expansion of ports.

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jovenlim89

jovenlim89

Sat Sep 05 2009, 06:58AM

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Thanks Ajay...If shift register latch just can expand 8 port by usinf 3 port, that mean that my PIC16F877A have 33port and use 3 for shift register latch.After expand, I will get 38 right? But if get 38 port, I still lack of 1 slot... Haha! Anyway..Thank you so much.. If you all got anymore way,please suggest here...Thanks~

Hope u all can help me~Thx..

ExperimenterUK

Sat Sep 05 2009, 11:31AM

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By port do you mean 1 pin or 8 pins ?
What do you need the extra pins/ports for ?.

jovenlim89

Sat Sep 05 2009, 08:47PM

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Omg...I am so sorry...I have wrong typing.. It should be pin...To get extra pin, I should have extra port right? I am planing to use the extra pin to make my lcd display..And also my matrix keypad... Anyhow, thank you so much! I am still new, I will make mistake frequenly.So sorry ExperimenterUK..

Hope u all can help me~Thx..

ExperimenterUK

Sun Sep 06 2009, 02:21PM

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jovenlim89 wrote ...

thank you so much! I am still new, I will make mistake frequenly.So sorry ExperimenterUK..

No problem

A port usually has 8 pins, so an extra port will give an extra 8 pins.
A simple shift register is probably be the best option, unless a slave PIC
would be useful to handle other functions of the project.

[ Edited Sun Sep 06 2009, 02:28PM ]