Eritreo.

The '420 reset's into it's default NON-PAGE Mode. In this mode it is not much different from the '320/'520.

According to the Dallas Mem. Xface Doc, Non-Page mode @ 11.0592MHz allows 242.77 ns. for mem. access. This also include the LATCH prop. delay time so 120 is ok. According to the same document 19.8MHz is the highest System Clock Fz. for 120ns.

You can find the doc @:

App Note 26: Ultra High-Speed Microcontroller Memory Interface Timing

regards,
p