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External Memory Interfacing with PIC MCU

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Mehmood Ahmed

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Hi,
I am new to PIC Microcontrollers. I want to interface PIC MCU with external RAM and PPI(8255, etc.), like we can interface on 8051 MCU. I will be very thankful if someone helps me in this regard.

Regards.
 
You are aproaching this from an 8051 viewpoint. Think PIC!

Most often you can choose a PIC with enough internal Flash, EEPROM and RAM to get the job done. Which is a good thing since most do not have an external memory interface. It is common to use I2C EEPROMS.

You can get PICs with 100 pins or more. There is no need for a PPI.
Note that DIP packages are limited to 40 pins but that will meet many peoples needs.
 
Hi,
I am new to PIC Microcontrollers. I want to interface PIC MCU with external RAM and PPI(8255, etc.), like we can interface on 8051 MCU. I will be very thankful if someone helps me in this regard.

Regards.

Yes, I agree with 3v0.

The only PICs I know that have an external memory interface are the big (18F8722) 84 pin thin quad flat package. These also have 128k bytes of program memory, and 4k of RAM, so you shouldn't have to worry about extra. :D
 
Hi,
I really apreciate ur help, and i agree that there is no need of external RAM but what if i need more I/0 ports and it is not feasible for me to use any PIC MCU except DIP40 which contains at most 4 I/O ports
 
Hi,
I really apreciate ur help, and i agree that there is no need of external RAM but what if i need more I/0 ports and it is not feasible for me to use any PIC MCU except DIP40 which contains at most 4 I/O ports

Then you can use a serial to parallel chip, such as 74hc595, or similar. Microchip also makes a serial to parallel converter, but I can't remember the number. There are many others.
 
The 8255 is positively ancient. You should look at I/O Expanders. The 74HC595 is ok but there is a lot more to choose from. Look at this maxim page: **broken link removed**
 
Not to mention it's an NMOS power sucker designed in the mid 70s for the 8085 product line. heh heh. I can remember using it and the 8259 interrupt controller. what a PITA. All sorts of error conditions and phantom interrupts.
 
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