Inherited designs are the worst. I recently got bitten by an Attiny somebody thought would work at 1.8V which it doesn't. Atmel is not afraid of putting lies in their datasheets :-(
-- Failure does not prove something is impossible, failure simply indicates you are not using the right tools... nico@nctdevpuntnl (punt=.) --------------------------------------------------------------
Perhaps, but kicking the crap out of a circuit helps to find flaws you missed. Besides, putting a simple yet effective test rig together is fun :-)
-- Failure does not prove something is impossible, failure simply indicates you are not using the right tools... nico@nctdevpuntnl (punt=.) --------------------------------------------------------------
I had wanted to do a 4 layer with full ground plane and split plane for 3.3 and 5V but got shot down. Mandate was for 2 layer Done in Eagle with 3.3V and 5V routed. Polygons top and bottom covering the whole board defined as ground. When a Ratsnest is done with orphans off, it will attempt to flood any free areas with copper plane. If it can't fill an open area because traces are blocking it, drop in a few vias to bring in the ground from the other side... I still print out the board one layer per sheet when done in B size, put it on the light table and look for where my power busses are actually winding up. Helps to show any deficient connections. On the screen, try to show the ground net and so much of the board lights up, it's actually difficult to pinpoint problems. I have Alpha Blending ON to better see superimposed layers but even so, it's difficult.
For troubleshooting, I used freeze spray just to get a ballpark temperature. Was also good for local cooling. I have some plastic shields I made in the shape of the chips in question so I could cool just one component or area at a time. It was definitely the ADuC841 that was cold sensitive when the decoupling impedance was deficient. Some lot codes were more sensitive than others but at least they were bona fide and not counterfeit devices as I had considered at one point.
The electrons were too cold to travel that far?
Putting an ADuC841 on a 2-sided board is, well, brave. Flooding unused areas on a 2-sided board doesn't help much. Tell whoever "shot it down" to make it work.
-- John Larkin, President Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
I routinely use it's bigger brothers, the ADUC70xx series on two-layer boards with no issues. I like to use one layer for groundplane (as continuous as possible) and the top layer for routing. Re-allocate the I/Os where possible to get an easier layout. And decouple noise-generator and noise-susceptible parts locally with R/C or L/C filters (depending on current and permissible voltage drop).
Thanks,
-- John Devereux
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