Programming the SX using less than 5V

DosManDan

Can the SX28 only be programmed at 5V? I'm working with an ISD4004 sound chip that runs on 3V, so I'm running the SX28 at 3V too in an attempt to avoid voltage difference issues. I hooked up the SX Key to program it and it doesn't see the SX chip. I changed the power back to 5V and it works fine.

After programming it, the SX seems to run fine on 3V, but I can't keep unhooking it everytime I need to change the code. According to the specs, the ISD4004 MOSI, SCLK, INT, RAC and SS pins will all handle 5V even though the rest of the chip runs at 3V. However, the MISO still runs at 3V and needs a few components to work at 5V. Should I give up and run two power supplies (5V and 3V) and wire up the MISO to handle 5V?

If you are interested, the specs are at:

http://www.winbond-usa.com/products/isd_products/chipcorder/applicationbriefs/apbr25a.pdf

Ideas?
Dan

Sparks-R-Fun

The SX can run and be programmed at 3V but… the SX-Key needs five.

The Parallax SX KeyRing is what you need.

- Sparks

DosManDan

Figures I just made an order with Parallax Monday! Guess I'll drive over there at lunch and get it tomorrow.

Thanks alot for that info, I read about those long ago and forgot they existed. Does anyone know why they are being discontinued and are they going to have a new product? Maybe an all in one SK Key?

After running into the probs I'm having with this voltage difference, this will be a real time saver for me.

Hey, this just occured to me, can I just pump 5V into the SX Key (since I have it), 3V into the SX28·and just run the OSC1 and OSC2 pins to the SX? Literally, this would be a one wire change for me.

Thanks!
Dan

Post Edited (DosManDan) : 3/28/2007 9:38:55 PM GMT

Sparks-R-Fun

DosManDan,

If you decide to provide regulated 5V power to the SX-Key, you must assume all risks to possible damaging results. With that being understood...

the SX KeyRing Manual said...
The SX KeyRing provides a pass-through for Vss, OSC1 and OSC2. The Vdd connection is isolated; providing +5 volts DC to the SX-Key through its 5-volt regulator. The SX chip being programmed should have its own Vdd connection that can be any voltage within the range specified in the SX datasheets. For example, the SX chip can be operating at 3.3 volts while the SX-Key (plugged into the SX KeyRing) is operating at 5.0 volts.

You will have to form your own conclusions but if you try it, do not skimp on the power supply. The SX KeyRing manual recommends the use of a 1A power supply. Some of this obviously is transformed into heat by the voltage regulator but if you skimp on the available power you may experience undesirable results.


- Sparks

Wilton

1.· Actually the SX-Key is quite picky.· I have an application with a multiple output SMPS and the CPU power is on an output that is not directly regulated.· It is fine unless the output with the feedback has no load, in which case the CPU power drops to 4.5 to 4.7 V, which is fine for operation, but WON'T program.· The SX-Key fails unless I insure there is some load on the other output so the CPU gets closer to +5, which is a pain since a reset SX default state removes all the loads on the other supply.· Of course, since the SX-Key draws power from the CPU supply, that makes the effect even more pronounced.

2.· Powering an SX-Key separately is a bad idea, because the output voltages it provides are going to be based on that 5V.· If the SX is like most ICs, at least one of the pins in question has a diode to Vcc that is normally reversed biased, but becomes conductive if the pin goes more than .7 volt above Vcc.· This would pull the application up to > 4 V and probably burn out the diode and associated bond wire in the process because they aren't designed to sustain that much current.· Destructive latchup is another possibility!

DosManDan

Thanks for the notes, I checked here last night before continuing and there weren't any answers so I forged ahead...here are the results.

I am using the recommended 12V power supply with the PDB, so it has enough power to run everything so far.

Using the PDB, I pulled 5V straight into the SX Key. I ran the OSC1 and OSC2 to the SX chip and had the SX and other chips on the PDB running at 3V (I wired in a regulator for the 3V).

Everything seems to be working fine. I hooked up the USB Oscilliscope and watched the volts to make sure I wasn't getting any unexpected results.

If I have time tomorrow, I'll drive up and buy a SX Key Ring and do it properly. Would you recommend I stop doing development until then, or does it sound like I can keep going?

Thanks again,
Dan

Sparks-R-Fun

DosManDan,

Assuming that Vss (which you did not mention) is shared as a common connection between the PDB, the SX-Key and the rest of your 3V SX circuitry it sounds to me like all is good. I consider the fact that it is working (and I know of no reason why it should not) to be a good sign! I see no reason to stop.

- Sparks

DosManDan

Sorry about that, yes, they are all connected to the same Vss. I took a pic of the PDB with everything hooked up. I'll post it up once I get the pics off the camera.

Running into another problem, which is the quality of sound from the ISD4004. Real weak and not the quality I was looking for.· But I'm happy as heck I got it working and can record and play sound.

It has such a low voltage input (30mv PP) and can't take a line output from a sound card. Thinking I need to make an attenuation circuit to bring the volts from 2V down to 30mv using a 100:1 ratio.

Any thoughts? As always, thanks for all of your help.
Dan

·