MAXQ612/MAXQ622 User’s Guide
2-14 Maxim Integrated
2.5.3 Memory Mapping Rules
When executing program code in a particular memory segment, the same memory segment cannot be simultaneously
accessed as data.
The following is a summary of the memory mapping rules.
• When executing from the normal user code segment:
The lower 32KWords program space (P0 and P1) is always executable as program.
The upper half of the code segment (P2 and P3) is accessible as program when UPA is set to 1.
The utility ROM is an extension of the program space if the UPA bit is 0.
The physical data memory is available for access as a code segment with offset at 0A000h if the UPA bit is 0.
Load and store operations to data memory are executed normally when addressed to the physical data memory.
The utility ROM can be read as data, starting at 08000h of the data space.
• When executing from the utility ROM (only when UPA bit is 0):
The lower 32KWords program space (P0 and P1) functions as normal program memory.
Data memory is available for access as a code segment at the upper half of the program memory map, immediately
following the utility ROM segment.
Load and store operations to data memory are executed normally when addressed to the physical data memory.
P0 can be accessed as data with offset at 08000h when CDA[1:0] = 00b in byte mode or CDA1 = 0 in word mode.
P1 can be accessed as data with offset at 08000h when CDA[1:0] = 01b in byte mode or at offset 0C000h when
CDA1 = 0 in word mode.
P2 can be accessed as data with offset at 00000h when CDA[1:0] = 10b in byte mode or CDA1 = 1 in byte mode.
P3 can be accessed as data with offset at 00000h when CDA[1:0] = 11b in byte mode or at offset 0C00h when CDA1
= 1 in word mode.
• When executing from the data memory (only when UPA is 0):
Program flows freely between the lower 32KWords user code (P0 and P1) and the utility ROM segment.
The utility ROM can be accessed as data with offset at 08000h.
P0 can be accessed as data with offset at 0000h when CDA[1:0] = 00b in byte mode or CDA1 = 0 in word mode.
P1 can be accessed as data with offset at 0000h when CDA[1:0] = 01b in byte mode or at offset 04000h when CDA1
= 0 in word mode.
P2 can be accessed as data with offset at 00000h when CDA[1:0] = 10b in byte mode or CDA1 = 1 in byte mode.
P3 can be accessed as data with offset at 00000h when CDA[1:0] = 11b in byte mode or at offset 0C00h when CDA1
= 1 in word mode.
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