Additional I/O - AMSTRAD cpc 6128 User Instruction

The example below shows this scheme in operation when HIMEM is lowered in
conjunction with loading an RSX.
100 SYMBOL AFTER 256
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coLLapse user defined characters
110 rsxaddress=HIMEM-rsxLength
120 MEMORY rsxaddress-1
130 LOAD "rsxcode",rsxaddress
140 CALL rsxaddress
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Log on rsx
150 SYMBOL AFTER 140
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restore user defined characters
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FIRM WARE DATA AREA
JUMP BLOCK
BASIC DATA AREA
DISC ROM DATA AREA
ANY OTHER RQMS' DATA AREA
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Memory Map with RSX loaded in recommended position
Additional 110
Most I/O port addresses are reserved by the computer - in particular, addresses below
&7FFF should not be used at all.
For your reference ....
Chapter 7 Page 47