MBSEQv4 LPC17 display problem

MIDIbox SEQ
21

Thank you!

 

this problem seems to be related to an undocumented silicon issue: the pins which are used to drive the E1/E2/RW/RS line are 5V tolerant (according the the user manual), but the voltage level is limited to 3.3V in open drain mode, probably because of internal protection diodes.

 

Actually the external pull-up resistors should pull the level to 5V - and this causes a short circuit, which gets worse (and also affects neighbored pins) than more displays are connected.

 

Configuring these pins for push-pull mode helps to avoid the shorts - and fortunately the 3.3V output voltage at logic-1 is still high enough for the LCDs! :slight_smile:

 

Best Regards, Thorsten.

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Hi ilmenator,  I had the same issue but with a smt32,  one LCD works fine, both -> garbage. It appears when suply voltage with the PC through USB cable, and fix it changing a 74HC595 with a 74HCT595 instead. so now it’s working fine, but what you wrote ( and what Thorsten wrote ) is very important to me to understand the problem, may be a voltage level problem? in my case it seems i think due to the use of a 74HCT595, I’m not sure

 

 

 

Thanks to Thorsten and you for this contribution

 

 

Albert

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