DAC malfunction, or PIC problem?

lyndia · Joined: 19 Jul 2009 Posts: 5

I'm using a TI TLV5639 12bit DAC chip and having the following problem:

The lower 8 bits seems to function, although not too accurately. Once I use any bit higher than that the analog output just jumps to the supply voltage (not even the reference voltage). The thing is that I used PORTC for the lower 8 bits, and a few bits from PORTA for the higher 4 bits. I was wondering if the usage of a different port could've affected anything.

It's my first time using DAC chips. Thanks to anyone who'd give some idea as to what might be wrong.

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

The data has to be written in two separate operations. There will be a
glitch in the output, for that reason.

Why are you using a parallel-interface DAC ? Most people would use
a chip with a serial-interface, unless maximum speed is needed.

lyndia · Joined: 19 Jul 2009 Posts: 5

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

If you want hi performance and blazing throughput with very LOW code space usage and low instrux cycle overhead , you can't beat parallel AD/s and DAs

I use both kinds of parts in a combined analog /digital servo for an implantable , magnetically levitated bearing system ( no bearings or physical rotor contact inside the pump - just coils and magnets ) - that employs back emf 3 phase "brushless" rotation to over 5000 rpm - and yes Parallel A/d and D/a because speed is paramount for stability.

In the end - the PIC 18F design was able to be down graded to a lowly 16f887 and runs quite perfectly at a blazing A/D conversion rate - using only the 8 mhz internal oscillator.

I use and endorse both the ADS8517 and the ADS8371 (which with a 1 shot trick trigger circuit externally) , requires just 12 instructions to retrieve 16 bits of superb quality data.

Yes Virgina - there ARE very good reasons to use parallel DACS and A/Ds