Need more than 2 Uarts?

burnsy · Joined: 18 Oct 2003 Posts: 35 Location: Brisbane, Australia

Hi There,

I'm currently working on a project where I have about 4 serial devices (1 swipe reader, 1 VGA controller, 1 GSM module and a serial keypad)connected to my 16F877 based controller board.

To achieve it, I use the onboard UART and 3 x 16F687s, each one of them acting as a UART via the SPI interface. Its less expensive than a MAX3100 and reliable. The 16F687's can even provide additional I/O.

I wrote this code long ago, and was wondering if anyone is interested in me posting it in the code section. If it's useful, let me know and I will.
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kender · Joined: 09 Aug 2004 Posts: 768 Location: Silicon Valley

It would be interesting to see your code – distributed architectures are fun.

BTW, NXP now makes I2C UARTS - SC16IS752. They are cheaper than MAX3100, they are dual, they use I2C, which saves pins.
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ckielstra · Joined: 18 Mar 2004 Posts: 3680 Location: The Netherlands

asmallri · Joined: 12 Aug 2004 Posts: 1635 Location: Perth, Australia

It is always interesting to see how other solutions are built.

Another option is to use 1 x PIC24FJ64GA004 (40 pin) and 1 x PIC24FJ64GA002 (28 pin) to replace all 4 PIC16F in this scenario. These PIC24Fs have mappable I/O (about time) with each giving you two UARTS and two SPI ports. This also gives you a lot more RAM and PGM memory and enhanced peripherals.

This would deliver a lower cost solution with smaller PCB footprint. Of course you then need a compiler upgrade :-)
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donquixote · Joined: 21 Jul 2008 Posts: 15 Location: Shanghai, China

Is it possible to use the PIC24F128GA106 in the multi-uart solutions?

I am working on the design with 3 UARTs which migrated from PIC16F873A.

Thanks.
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Don Quixote

asmallri · Joined: 12 Aug 2004 Posts: 1635 Location: Perth, Australia

burnsy · Joined: 18 Oct 2003 Posts: 35 Location: Brisbane, Australia

Well, there's a few good suggestions there that I'll be looking into myself.
I like the I2C solution by NXP, although being old-school I would really still like to use 5V and through-hole parts.

I might try the PIC24F128GA106 as that seems like a good alternative, but yep, I would have to buy a new compiler ;).

The solution I came up with the multiple 16F687s is one designed years ago when the 16F687 became available, but was never utilized. Recently, I was asked to design a new project with multiple uarts, and I dug the pcb out of the store-room and continued writing for it. I have some code written for the 16F877A and 18F4520s, either used as a master processor, and of course the 16F687s as slaves. I do like using the SPI as opposed to the I2C in this application as the processor overhead is minimal, and is all interrupt driven.

I'll be finishing the code over the next week or two. I'll post as soon as I can and include circuits etc..
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This is the last code change until its ready....