As you can see in the component datasheet, low speed PWM mode you need an additional external series resistance of 100k-1M.
Translation of his question.
As the title, I am in the use of Low-speed mode driver LCD difficulties, LCD can not be normal display, should not show the part is also displayed, adjust the contrast and refresh frequency has not been able to eliminate the abnormal phenomenon. And I in the high-speed mode display is normal, how can I locate the problem, what is the solution? Exceptional, Low-speed mode-driven LCD has no case to provide reference? Thank you!
Please post your code by selecting file and then create Work_Space_bundle and attach the program to a new comment. Also Please let us know what the part number of your :LCD is.
I am guessing, but are you referring to the Cypress LCD component? http://www.cypress.com/file/185426/download
If you attach a minimal work space bundle of your project, it would be easier to debug starting from there.
You may need to change settings when switching between low-speed and high-speed modes. A reference to the LCD part number would help with this, as we don't know which one you are referring to.