Bitfields for Intel 82437VX,82439HX/TX DRAM extended control register:
Bit(s)	Description	)
 7	reserved
 6	(VX/TX) refresh RAS# assertion length (0=4 clocks, 1=5 clocks)
 5	(VX/TX) Fast EDO Path Select
 4	Speculative Leadoff Disable
 3	(82439HX) Turn-Around Insertion Enable
	=1 insert one extra clock of turnaround time after asserting MWE#
 2-1	Memory Address Drive Strength
	82437VX:	     82439HX:		       82439TX:
	  00 reserved	       00 8mA			 00 10mA/10mA (MA/MWE#)
	  01 10mA (default)    01 8mA/12mA (MAA/MWE#)	 01 10mA/16mA (MA/MWE#)
	  10 16mA	       10 12mA/8mA (MAA/MWE#)	 10 16mA/10mA (MA/MWE#)
	  11 reserved	       11 12mA			 11 16mA/16mA (MA/MWE#)
 0	(82437VX) DRAM Symmetry Detect Mode
	(used to force some memory address lines to fixed value for detecting
	  DRAM symmetry row-by-row)
 0	(82439HX) 64MBit Mode Enable
	=1 enable support for 64M SIMMs
 0	(82439TX) reserved
SeeAlso: #01099,#01108,#01098,#01116