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PIN 39 (A17)--+ O---- Vcc +5v (Switch pos 2)
ROM 1 (LW) | .
PIN 39 (A17)--+ O---- Ground (Switch pos 1)
ROM 2 (HW)
*Pins 39 bent outside sockets
*ROM selector jumper set to default (1-2)
With switch on pos 1, lines A17 are grounded, only lower 512KB usable
With switch on pos 2, lines A17 are selected, only upper 512KB usable
I used following program to build the ROM image :
FOR i=0 to (1024*1024)-1 : POKE a+i,255
Then, I processed the ROM image file with WROM_BAS program supplied with SMSQ/E to split ROM file in LowWord and HiWord files and burned them on the M27C4096 ships.
This worked nicely and permitted :
-Confirm usage of 1MB ROM size on Q40
-ROMing of recent SMSQ/E versions greater than 256KB
-Alternative DIY ROM selector working with any ROM size