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New Project wp34s micro usb flash cable revisited
02-08-2015, 04:58 AM (This post was last modified: 02-08-2015 06:59 AM by matthiaspaul.)
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RE: New Project wp34s micro usb flash cable revisited
(02-05-2015 12:14 AM)BarryMead Wrote:  
(02-04-2015 11:03 PM)matthiaspaul Wrote:  Does someone know if the calculator's RX and TX signals are ESD protected already?
The HP-20b/HP-30b schematic shows that the serial inputs are connected with jumpers (JP5, JP6) directly into inputs/outputs on the processor. So the only ESD protection would be the standard I/O input protection diodes on an ARM micro-controller input/output. (Not much)
Thank you, Barry. I have meanwhile found the HP 30b schematic and SDK as well.

From personal experience (with other designs), I would not want to rely on the CPU's internal clamping diodes alone when directly exposing I/Os to a connector. I've seen too many chips partially or fully blown out due to ESD outside the lab environment. Therefore, I'd like to recommend to add protection diodes at least to the two data lines.

Greetings,

Matthias


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RE: New Project wp34s micro usb flash cable revisited - matthiaspaul - 02-08-2015 04:58 AM



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