Forward Progress in MDAC land!!!

frank freedman

Forward progress in MDAC land using PASM now for speed. With SPIN, a 4096 step ramp w/ fixed Vref was taking about 2+ seconds to generate. Now with PASM, it does it in 18.6mS. Just a hair over the vertical ramp speed of NTSC. So with fewer steps, this would have made a great programmable vertical sweep generator back in the day. (CRT for the kiddies out there).

The two photos are the 4096 step ramp w/ a fixed Vref (dac out and ~10x amp out), and the second is the same 4096 step ramp with the Vref replaced by a 3Khz sine wave (same x10 output as fixed Vref). Hmmmm, wonder what I could do with a sawtooth either into Vref and a generated ramp or a generated sawtooth with a programmable Vref and say a comparator....... PWM???? Who knows what else.

Next trick will be getting it to repetitively read out a buffer in the hub and see where the speed limits are on that one. Maybe given the tables in rom, create and generate from tables in hub, arbitrary waveforms. With some packing trickery, maybe double 12 bit words per each long and dump them into the cog for speed on output.....

Yeah, this will become another object when I have finished playing with it. The LTC8043 is a really simple device to interface. Not really SPI, more of a simple shift register with a /load pin. Clock the bits in and drop /LD and the value is there with a fairly fast settling time.

Frank

Ahle2

What will you use the LTC8043 for that the duty DAC can't do?

frank freedman

Not sure what type of DAC you are referring to, but at the moment I am playing around with some audio processing ideas. One type of DAC can be used for just that, making a analog voltage from a digital value. Some one recently mentioned an Microchip Inc device, and a few months back, I had built up an R2R DAC (ikalogic 8bit repurposed to 12 bit). It was used to convert values captured from an MCP3201 back to analog.

One possibility for the MDAC is putting the signal into the Vref pin, and configuring the DAC to provide a set output from 0 to N gain in 4096 steps. These devices have a number of uses in control circuits such as providing levels for kv and filament heating of ac power in medium and high frequency x-ray generators and other systems.

But mostly playing to learn, so not running any particular purpose as opposed to any other DAC

Frank

evanh

frank freedman wrote: »

The LTC8043 is a really simple device to interface. Not really SPI, more of a simple shift register with a /load pin.

That's pretty much all that SPI is. Ok, so it's missing a data out pin for daisy chaining but that's hardly a requirement for SPI. Labelling something as SPI is only saying it has a shift register with unidirectional pins and separate clock pin. Everything else is optional and the masters are usually highly configurable to fit the myriad of non-configurable slaves out there.

EDIT: And the hardware framing using a load pin is also standard. Without the load pin you would be heading away from SPI.

evanh

When I wrote my first industrial assembly I tried to use an external eeprom for parmeter store but failed and ended up using a chuck of internal eeprom (in the days before flash) instead. Luckily, the HC11 allowed self erasing/writing to individual bytes of program space.

I never did solve why I botched using the SPI part but quite possibly I had the command ordering wrong due to not following what was happening at power up ... I don't remember explicitly trying this possibility even though it seems a really obvious step now.

The LTC8043 doesn't have commands or addresses so that complexity is eliminated.