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chapter 7
PROGRAMMING AUXILIARY MEMORY
MultiRam C’s memory is addressed by The Apple as standard auxiliary memory.
Therefore, when any 64K bank of the MultiRam cards memory has been switched
into place as active auxiliary memory, standard auxiliary memory addressing
techniques can be used to access MultiRam C memory.
This section briefly reviews standard auxiliary memory programing techniques
for the Apple //c. For a more detailed description of auxiliary memory
programming for the Apple //c, please refer to The Apple //c Reference Manual
published by Apple Computer, Inc.
If you are familiar with programing auxiliary memory, you may wish to go
directly to Chapter 9. To fully use all of the MultiRam card’s memory as
auxiliary memory requires switching from one bank of MultiRam 64K auxiliary RAM
to another, by means of one soft switch. This is detailed in Chapter 9.
To access auxiliary memory from a program, to transfer program control or move
data to auxiliary memory, or to employ double high resolution graphics, requires
assembly or machine language programming skills. The following discussion
assumes these skills.
GENERAL INFORMATION
The Apple //c uses a 65C02 microprocessor to control its operation. This
microprocessor can address only 64K of memory at one time.
The //c contains two banks of memory: 64K of main memory and 64K of auxiliary
memory. To use the 64K auxiliary memory, the //c uses a set of soft switches,
contained in its Memory Management Unit, to control the address bus and switch
between the 64K of main memory and the 64K of auxiliary memory. The soft
switches are in turn controlled through software.
The 64K of auxiliary memory may be used for program or data storage, except for
1K which is used to control the 8O—column display. If you are going to use only
4O—column mode, you say use the full 64K.
The video display of the //c is controlled by routines located in specific areas
of memory. In 4O—column mode. Text Page 1 and Text Page 2 control text and
l0—res graphics display in the main memory (see Table 8.1 for locations). For
80—column mode, Text Page 1 of both main and auxiliary memory control the
display.
Double High—Resolution Graphics may be turned on via soft switches. This
doubles the horizontal resolution of Graphics Page 1. To turn on the double
hi—rem graphics, write any value to soft switch 80COL ($C00D), TEXT Off ($C050),
HIRES On ($C057). and MIXED Off ($C053).