Installation manual

Chapter 3
TESTING AND TROUBLESHOOTING
This chapter covers the testing procedures you may use to check the RAM on
your MultiRam RGB card.
All those who just installed a MultiRam RGB card or added memory to it
should read this chapter. Refer back to this chapter and the diagnostic memory
test, which is on the back side of the MultiRam disk, whenever you doubt the
RAM on the MultiRam RGB card.
Memory Bank versus RAM Bank
Just to keep everyone together let’s define two similar sounding but very
different terms that are used when talking about memory cards.
Memory banks refer to the addressing of the Random Access Memory (RAM)
chip. A memory bank has an address range of 0 to 65535 (decimal), referred to
as 64K, and a bank of RAM chips may have one or four memory banks in it.
The microprocessor used in the Apple //e is the 6502 (non-enhanced) or the
65C02 (enhanced) and is able to address only 64K of memory at a time. By
electrical slight of hand, Apple has the microprocessor find and use 64K of
motherboard memory. 12K of ROM memory, 4K of input/output, and 64K of
memory on the AUX 80 column card. That’s 144K total. This slight of hand
is called bank switching which enables the 6502 in find and use far more
‘memory’ than what the microprocessor’s designers intended it to. Checkmate
Technology extends this slight of hand and has the microprocessor find sixteen
memory banks on the MultiRam card instead of the standard one bank. These
sixteen memory banks are contained in four RAM banks, using 256K chips.
A complete RAM bank is a set of eight RAM chips that may be either 64K or
256K in size. The MultiRam RGB card has sockets to accommodate up to
four RAM banks. Mixing 64K and 256K chips in a single bank will result in
only 64K of useable test memory and will crash application programs.
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