On Tue, 2013-11-12 at 22:45 +0000, joem wrote:
On Tue, Nov 12, 2013 at 7:51 PM, joem joem@martindale-electric.co.uk wrote:
Try this :) it popped up on Google pretty quickly --> http://www.hobbytronics.co.uk/schottky-logic-level-conversion
: awesome. done. added to spec.
Same problem - access to the 3.3V power line inside the EOMA needed.
| no it is not. TTL 3v logic is somewhere around 2v for low. a small |reduction (such as using another shottky diode) would be enough.
Anyway - 3rd diagram added - modified version of Henrik's diagram for the EOMA: http://www.gplsquared.com/eoma_boot/eoma_boot.html#uart_repair
| great. 1.8+3.3=5.1 so the pull-up would be to 3.23V - enough to be |definitely below 3.3v.
Hmmmppp... pull ups don't work like you would expect under certain circumstances. I'm removing the 3rd diagram from here: http://www.gplsquared.com/eoma_boot/eoma_boot.html#uart_repair
I don't understand what the guy is trying to say - construct and test is one way to remove doubt.
Also I'm not sure if the second diagram i did here http://www.gplsquared.com/eoma_boot/eoma_boot.html#uart_repair will work under all circumstances. If the UART TX pin defaults to a high value, the pull up will still drive the EOMA. You would need to press <CR> a few times to send low pulses to get the EOMA to power down. Alternatively connect to the internal 3.3V of the CPU as in first diagram - but sadly no access to that wire that feeds the CPU with 3.3V through the 68 pins. (Connecting to external 3.3V is no good - it will reproduce the said problem again.)