NorthStar HORIZON Random Access Memory User Manual page 47

The Strobe Generator selects one of four rows of RAM
chips by generating one of four row address strobes:
RAS
generated depends on the memory address, the size of
the memory and in some cases, on whether or not the
First Quadrant option is selected (see Section 3-4).
On a revision B 64K or 48K board or on a revision E
board of the same size that does not have the First
Quadrant option selected, the memory address selects
the row address strobes as shown in Table 5-1.
Address Range
0000H - 3FFFH
4000H - 7FFFH
8000H - BFFFH
C000H - FFFFH
On a revision E 64K or 48K board that does have the
First
selects the row address strobes as shown in Table 5-2.
The effect of this option is to swap the position of
the RAS 1 and RASH signals and thereby change the RAM
chips corresponding to the first and last quadrants of
the memory address range.
HRAM
-
3, RA9 7, RAS
Chip Selection-64K OR 48K, First Quadrant Option
Inactive
Quadrant option
or RASH. The
Table 5-1
Row
Address Strobe
RAS 1
RAS 2
RAS 4
RAS 3
selected,
USER/TECHNICAL MANUAL
strobe that
RAM
Chip Locations
64K
1A-1J 1A-1J
2A-2J 2A-2J
3A-3J 3A-3J
4A-4J ---
the memory address
is
48K