The CY7C374U device is programmed through some of its I/O pins. The CY7C374i is programmed through its JTAG interface and is ISR (In-system Re-programmable) capable. It is just a die revision and is same as CY7C374 in form, fit and function. Unfortunately, we do not have the datasheet for the U part. However, you can refer to datasheet for the the Cy7C374.
The CY7C374U is an old obsolete device and was limited in production. This device is not recommended for new design.
Please be noted our entire Cypress CPLD product are Obsolete and not recommended for new design and development. For more information on CPLD product, please visit our webpage: http://www.cypress.com/go/cpld