Troubleshooting and Diagnostics
RAM can be visualized as a group of seven 1M byte blocks (plus a half-block), with each block
covering the addresses from MOOOOO to MFFFFF, where M is a hexadecimal number from 9 thru F.
For instance, the top 1M byte block covers the addresses from FOOOOO to FFFFFF.
Add-on RAM comes in two sizes, 1M byte (the 98257A card) and 256K bytes (the 98256A card).
The 1M byte card occupies a 1M byte block. The 256K byte card occupies one-quarter of 1M byte
1M Byte RAM Card Address
1M byte RAM card blocks cover addresses from MOOOOO to MFFFFF, where M is a hexadecimal
number from 9 thru F. A four-segment switch determines the address. For instance, this switch is set
Thus, this RAM card includes the addresses from 000000 to DFFFFF.
Checking a 256K Byte RAM Card Address
256K byte RAM card blocks cover addresses from MNOOOO to MTFFFF, where M is a hexadecimal
number from 8 thru
N is a hexadecimal number 0, 4, 8 or C, and T equals N plus three. A
six-segment switch determines the address. The left-most four segments of the switch determine the
value of M, and the other two segments (and two implied segments) determine the values of N. For
instance, this switch is set to 111101:
Thus, this RAM card includes the addresses from F40000 to F7FFFF.