LPC1769 QEICAP delay/decay

Discussion created by lpcware Employee on Jun 15, 2016
Content originally posted in LPCWare by paulctan on Mon Feb 27 14:08:29 MST 2012
I need some help with getting velocity measurements working properly.

According to of UM10360 Rev. 2,

QEICAP should be a copy of QEIVEL right after the last QEITIME expiry.

I have a test jig hooked up with a motor running around 100rpm and an US Digital E4P encoder.  QEICAP and QEIPOS work properly, *BUT* QEICAP values are decaying instead of instantly going to 0 when I stop the motor (yes, I physically stopped the shaft after stopping the motor, but QEICAP still showed decaying values!)

Is there some time averaging function going on with QEICAP?  If so, are there any docs on it that I may have missed?  Also, how do I disable it? 

I need to find the instantaneous (well almost instantaneous) velocity, however what I'm seeing is that QEICAP almost has a 1-2 second delay after the motor has stopped.  QEIPOS stops changing instantly though!! 

I want to use QEICAP instead of calculating the velocity based on QEIPOS (since you have it as part of the chip), but I need help!


Paul Tan.