Request for the ZX.... only issue I've found...

[Genesis]

... is the regulator used on-chip.

Parallax is using a very nice low-dropout reg that provides the ability to do something that's kinda important to me - shut off peripherals when the unit goes to "sleep", thereby making a micropower mode possible.

Here's the issue and application....

Battery powered device. When its active, it draws significant current - bursts in the 250ma range, "normal operating" in the 50-60ma range. On a set of 5 AA NiMH cells (6V nominal input) you can get in the area of 40 hours of operation running before I get down to 5.5V and a brownout condition.

But - under certain conditions its ok for the unit to go to "sleep", shutting off all peripherals (LCD, etc) and then monitor inputs periodically for a condition that requires it to "wake up."

What I'm doing with the Parallax product is using the internal regulator (on chip) for the processor, but using one of its I/O lines to control an inhibit on my off-chip regulator for all the peripheral circuitry. I can thus shut down the outboard circuitry and the Parallax chip plus the regulator draw roughly 100ua in this mode - very little - which radically extends battery life when in "standby."

Every couple of seconds I power up the peripherals, check for conditions that require the unit to go active, and go back to sleep. This requires only a few milliseconds (mostly settling time on the peripherals once powered back up.)

It appears the ATMEL chip can be put into "sleep" mode, BUT the regulator on-chip doesn't have a recognizable part number on it I can cross-reference and from the input specs (e.g. 7V minimum voltage for proper regulation) this won't work off a 6V supply.

I'd really like to use the ZX for this application (my initial look at it indicates it will work - I've got all the I/O code working on the same PCBs), but the lack of being able to do power control is a big deal......

Any hope of this being something that would be addressed? The ZX24 is a good product for me mostly due to formfactor - the 40 is too big (I have severe size constraints on this product.)

[dkinzer]

The on-board regulator is a ua78L05. It was chosen for its wide operating range that makes it more robust for less experienced users. It is true that the drop out voltage is higher than many other regulators but this was considered an equitable tradeoff for the full spectrum of likely users. The on-board regulator is capable of supplying 100mA and that includes the power drawn by on-board components.

For all but the simplest applications an external regulator will be needed and the ZX can be powered via pin 21 using the external regulator. You can choose a regulator that meets all of your needs - dropout voltage, quiescent current, maximum current, accuracy, etc.

[Genesis]

I think you missed where I'm going with this.....

I can run with an external reg just fine (and am), but then I can't shut that reg off, because that's the same one that powers the peripherals.

I guess I could run a SECOND external reg just for the CPU...... was just questioning the reason for the selection that you folks made, because its characteristics make the "split supply" paradigm I'm using right now untenable.