Chapter 5-Using
RAMBO XL
Bit 4
RAME
When clear, this bit selects the bank determined by AO-A3 to
appear at the $4000-$7FFF window. When set, main bank RAM
will appear at this window.
Bit 7
DRE
When clear, this bank selects the diagnostic ROM to be
shadowed at $5000-$57FF. When set, the diagnostic ROM is
disabled.
Some Notes About Using the Extra RAM
If you do decide to use the extra RAM in your own programming,
please follow some of the following guidelines for compatibility and
fewer debugging headaches:
• Before enabling the RAM (setting RAME low), you should disable
both NMI and IRQ interrupts. NMIs may be disabled by setting
$D40E (NMIEN) to 0. Make sure that you reset it to $EO after
disabling the extra RAM. IRQs are disabled by the SEI
instruction
and enabled by CLI.
• Keyboard entry and SIO may not be used while interrupts are
disabled.
• If you are absolutely sure no interrupt handlers are at the
$4000-$7FFF window there is no need disable interrupts. Note
that if using the RAM as a RAMDISK, you may not assume this.
• Keep display lists and display data out of the $4000-$7FFF
window! When the extra RAM is in this window, ANTIC also sees
the extra RAM at this window. The 13OXE avoids this problem by
forcing ANTIC to main memory unless bit 5 is clear. If bit 5 is
clear, then ANTIC uses the memory bank selected by bits 2 and 3
on the 13OXE.
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