hey
i have small problem..
currently im using only 1mb of dram, but in some circumstances it fails and gives out bad output
basicaly construcion is based on freddy chip (internal construction of this ic is like shift register for CAS and RAS output and phi0 for cpu and ofcourse address multiplexer) but this is limited to 64k - adding another 74ls157 and 74ls393 (for refresh counter) and yet another 74f157 provided way to drive 1mb 30 pin simm module
since i know that drams consume loads of current i don't know if this erratic behavior is due to use 74f157 chip on output or maybe that i use 4mb simm module (pin a10 is grounded and not refreshed)

my goal is to drive 16mb of ram without use of any surplus asic (pld or cpld will be doing this)