Using big ROMs on Q40
Posted: Fri May 19, 2017 5:13 pm
With Peter Graf's indications and some AM27C4096 ships supplied by Derek Stewart, I realized a little circuit permitting to have a global ROM size of 1 MegaBytes on Q40 with 2 bigs OS ROMed together (up to 512KB each) and selectable with a case switch (3 wires, 2 positions) :
*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 :
a=ALCHP(1024*1024)
FOR i=0 to (1024*1024)-1 : POKE a+i,255
LBYTES win1_SMSQE_Q40_OS1_ROM,a
LBYTES win1_SMSQE_Q40_OS2_ROM,a+(512*1024)
SBYTES win1_SMSQE_Q40_ALL_ROM,a,1024*1024
RECHP a
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
Have Fun
Alain
Code: Select all
PIN 39 (A17)--+ O---- Vcc +5v (Switch pos 2)
ROM 1 (LW) | .
| .
+----O
| \
| \
PIN 39 (A17)--+ O---- Ground (Switch pos 1)
ROM 2 (HW)
*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 :
a=ALCHP(1024*1024)
FOR i=0 to (1024*1024)-1 : POKE a+i,255
LBYTES win1_SMSQE_Q40_OS1_ROM,a
LBYTES win1_SMSQE_Q40_OS2_ROM,a+(512*1024)
SBYTES win1_SMSQE_Q40_ALL_ROM,a,1024*1024
RECHP a
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
Have Fun
Alain