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EZ-USB Development Board Page -13

4.7 U2 -- 22v10 GAL

A standard 22v10 GAL provides general purpose “glue logic” on the board. It provides the AND

gate required to combine the PSEN and READ signals, adds memory map support, debug LEDs

and provides three spare outputs for customer defined functions.

4.8 Memory Maps

Figure 1-1. The four EZ-USB Dev Board memory maps. 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 Kilobytes of on-chip code and data memory, plus 48

Kilobytes of external RAM. The 8051 begins execution from internal RAM (the GAL sets

EA=0). Note that even though there is an apparent overlap between the internal 16 Kilobytes

and bottom 16 Kilobytes of the external RAM, EZ-USB disables RAM strobes for the bottom

16 Kilobytes, so there is no conflict. This EZ-USB decoding allows a standard 64 Kilobyte

RAM to be used without requiring external decoding to inhibit access to the bottom 16 Kilo-

bytes.

– The second column, “24K gap”, enables the external RAM only for access to its upper 32 Kilo-

bytes. 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).

MM1: out

MM0: out

MM1: in

MM0: out

MM1: out

MM0: in

MM1: in

MM0: in

jumpers

0x2000

0x0000

0xFFFF

Factory Default

24K gap

Ext Flash

Single Chip

on-chipon-chipon-chipon-chip

off-chip

off-chipoff-chipoff-chip

32K

Ext

RAM

Code

Data

64K

Ext

RAM

Code

64K

Ext

RAM

Code

Data

16K

RAM

Internal

C&D

16K

RAM

Internal

C&D

16K

RAM

Internal

C&D

16K

RAM

Internal

C&D

Not

Used

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Cypress Semiconductor FX2LP Guida di Installazione Pagina 17

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