pic selection

Prefekt · Joined: 21 Oct 2010 Posts: 85

Hello,

I have a project that needs 4800 byte for data at one time in the memory.
Until now, I only work with pic 16f and 18f.
And I have no experience wit 16bit PIC's.

What is the better way, use the 18f and store the data in the flash memory, or use a PIC24?

I need two big arrays with 2400 bytes. An Extern EEPROM is too slow.
Which 16bit PIC is popular?

Regards
Volker

temtronic · Posted: Wed Apr 06, 2016 11:50 am

A lot depends on what you're going to do with the data. Is it going to be 'constant' (never changing) or 'dynamic' (it changes or you alter it).
Perhaps use FRAM or even external CMOS RAM?
What about access speed? Maybe n SPI or I2C memory device will work ?
Arguably there's more here using 16 and 18 series parts than 24 or dsPIC series, so more/faster help with code.

Honestly need more information about the application and demands of the project.

Jay

asmboy · Joined: 20 Nov 2007 Posts: 2128 Location: albany ny

Look at the data sheet for the 18f87k22 chip

8.0 EXTERNAL MEMORY BUS

It allows external parallel static ram chips to be translated as if they were internal to the pic. Very fast access with this chip, so you could incorporate a fast 32k or larger static ram chip as if it was internal memory and still have lots of port pins left over.
BTDTGTTS it works...

newguy · Joined: 24 Jun 2004 Posts: 1907

You can opt for a dsPIC as well. I have experience with the dsPIC33FJ256GP710A. Nice processor with 30k RAM and 256k ROM.

Prefekt · Joined: 21 Oct 2010 Posts: 85

Thanks for the informations.

I get data from a bluetooth device (4200 bytes) and store this data in a external eeprom. The eeprom needs few seconds to write and read the data.
It's an 25LC640 eeprom.

I must send this data with RS232 in less than one second. And a read from eeprom needs to much time. I use the ccs read_eeprom and write_eeprom functions.

So my idea is to store the data in the internal data memory.
The data are constant.

Volker

newguy · Joined: 24 Jun 2004 Posts: 1907

If you use an SPI FRAM or MRAM external memory, you'll probably be able to do the store in the allowed timeframe. An FRAM or MRAM has an instantaneous write (no write delay like a conventional EEPROM).

asmboy · Joined: 20 Nov 2007 Posts: 2128 Location: albany ny

newguy · Joined: 24 Jun 2004 Posts: 1907

asmboy · Joined: 20 Nov 2007 Posts: 2128 Location: albany ny

gpsmikey · Joined: 16 Nov 2010 Posts: 588 Location: Kirkland, WA

Prefekt · Joined: 21 Oct 2010 Posts: 85

I think I will try a FRAM.

Are there popular FRAM's which you used often?
I found the M25W256-G FRAM from Cypress, seems good for my demand.

temtronic · Posted: Tue Apr 12, 2016 5:34 am

As for PIC choice..consider one with TWO Hardware UART AND TWO hardware SPI peripherals. Something like the 18F46K22. Maybe there's a similar 16F PIC. To do all the data transfers you'll NEED hardware peripherals and interrupts otherwise you stand a good chance of losing data while the PIC is busy. You'll also need speed when you look at the 'path' the data has to follow.

Better to buy a more more powerful PIC now than waste a LOT of time trying to 'tighten' code, redesign PCBs, etc. You'll always need a couple extra I/O pins (LEDs, debug port) and memory (programs always get bigger !).

As for FRAM, I'd get a 16KB unit. Create a buffer of 'data-from-BT' and a 2nd buffer 'data-to-PC'. Use interrupts and data transfers will work 'in the background' while the PIC does 'other things'.

Jay

Prefekt · Joined: 21 Oct 2010 Posts: 85

Is there a driver available for FRAM?
I found a driver for Ramtron FM24C256, but this chip is no longer available. Cypress FM24W256 seems the follower for the FM24C256.
Can I use the driver for FM24W256 or is there another FRAM driver?

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

Research the topic. Type this into Google:

Prefekt · Joined: 21 Oct 2010 Posts: 85

The FM24W256 works and it's fast! Very Happy

Thank you for your help!