Basic does not convert well to ASM. You'd be better off building the code from scratch in ASM, it's not overly difficult to send data to an LCD in 4bit mode using a single I/O port. Check out AVRbegginers.net The site hasn't been updated recently but it has ASM code for a mega8 using the 4 bit interface which should be easy enough to convert to other AVR's. The interface description include character generator memory (reading and writing) is easily found searching on google.