On 17 May 2007 at 22:02, r.stricklin wrote:
Can somebody send me the decoded switch settings for
the 8-bit IBM
"64-256KB MEMORY CD"? There are 8 switches, marked A16-A19, 64KB,
128KB, 190KB, and 256KB.
The switches are exactly what they say they are.
Switch 1: On: A19 = 0; Off: A19 = 1
Switch 2: On: A18 = 0; Off: A18 = 1
Switch 3: On: A17 = 0; Off: A17 = 1
Switch 4: On: A16 = 0; Off: A16 = 1
Switch 5: On: 64KB installed on board
Switch 6: On: 128KB installed on board
Switch 7: On: 192KB installed on board
Switch 8: On: 256KB installed on board
Okay, so let's assume that you've got the original 5150 with 64KB of
planar memory installed. Further, let's suppose you've populated the
memory expansion card with 4 64K memory modules for a total of 256KB.
You'd set the switches as follows:
Switch 1 = On, Switch 2 = On, Switch 3 = On, Switch 4 = Off
Switch 5 = Off, Switch 6 = Off, Switch 7 = Off, Switch 8 = On
This would map the expansion RAM starting at address 1000:0 and it
would extend up to (but not including) address 5000:0.
This adapter requires the goofy 32-pin IBM 3-supply 64K modules.
Neither the adapter nor the modules are very common in my experience.
Cheers,
Chuck