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26 EZ-USB Development Kit User Guide, Doc. # 001-66390 Rev. *D
Advanced Development Board
3.8 Memory Maps
Figure 3-1. Four EZ-USB Development Board Memory Maps
Note The GAL sets EA=1 for the Ext Flash configuration only, enabling external code memory.
The factory default is to have both MM1 and MM0 jumpers removed. This setting should be used for
all development work using the Keil software tools.
■ The default configuration provides 16 KB of on-chip code and data memory, plus 48 KB of exter-
nal RAM. The 8051 begins execution from internal RAM (the GAL sets EA=0). Although there is
an apparent overlap between the internal 16 KB and the bottom 16 KB of the external RAM,
EZ-USB disables RAM strobes for the bottom 16 KB, so there is no conflict. This EZ-USB decod-
ing allows using a standard 64-KB RAM without requiring external decoding to inhibit access to
the bottom 16 Kb.
■
The second column, “24K gap”, enables the external RAM only for access to its upper 32 KB.
This configuration is useful for systems that add external devices that require memory-mapped
access. As with the default configuration, the 8051 begins execution from internal RAM (the GAL
sets EA=0).
■ The third column, “Ext Flash”, allows a flash memory (or other ROM) to be connected to the 8051
bus. This is the only configuration that starts 8051 execution from external memory (the GAL sets
EA to ‘1’). Because external memory occupies the bottom 16K, the internal EZ-USB RAM is
addressed only as data memory, instead of the combined program/data memory in the other
three configurations.
■
The fourth column, “Single Chip”, disables all external memory. This configuration is useful for
testing the final code to ensure that it does not use external resources present in the develop-
ment environment.