Minimig SDram

Advantages:
 * Cheaper and more memory.
 * Run faster : a 114 Mhz Chip-RAM is possible.
 * Consume less FPGA I/Os (especialy the DDR-SDRAM)

Disadvantages:
 * Uses pipeline (complicated!)
 * PCB traces must have the same length and a 50 ohm impedance.

jkonstan 070801:
 * The UB & LB strobes on the SRAM are due to data bus addressing needed for the 68K cpu. 68K CPU has UDS* strobe for upper byte lane D15-D8 access, and 68K CPU has LDS* strobe for lower byte lane D7-D0 access. When 68K does a read, D15-D0 can be accessed as a word with 68K reading what it requires off of its Databus; however, a write access on a 68K CPU requires the byte lane be qualified. When UDS* active on a write cycle, UB* on SRAM must be active. When LDS* active on a write cycle, LB* on SRAM must be active.
 * D15 ........D8,,,,,,,,,D7........D0
 * Byte 0= Even,,,,,,,,Byte 1= Odd => (Word 0)
 * /UDS ,,,,,,,,,,,,,,,,,,,/LDS
 * /UDS ,,,,,,,,,,,,,,,,,,,/LDS