Jameco Electronics 2000, 3000 manual xpc window stack

Models: 3000 2000

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xpc window stack

fetching an instruction from memory and fetching or storing data in memory. When enabled separate I and D space make available the combined root and data segment, typi- cally 52k bytes for root code in the I space. In the D space, the root code segment part of the D space is typically used for constant data mapped to flash memory while the data seg- ment part of the D space is used for variable data mapped to RAM. Separate I and D space increases the amount of both root code and root data because they no longer have to share the same memory, even though they share the same addresses.

64k

56k

52k

xpc window stack

20 Bit Memory Space

RAM

512k

 

 

 

 

 

 

 

 

 

D Space

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

I space

Data Segment

Root

Code

Root Segment

Flash 128k Manual background

64k

Variable D Space

Constant D Space

Figure 3-6. Separate I and D Space

Normally separate I and D space is implemented as shown in Figure 3-6.In the I space the root segment and the data segment are combined into a single root code segment. In the D space the segments are separately mapped to flash and RAM to provide storage for con- stant data and variable data. The hardware method to achieve separate 20 bit addresses for the D space is to invert either A16 or A19 for data accesses. The inversion may be speci- fied separately for the root segment and the data segment. Normally A16 is inverted for data accesses in the root segment. This causes data accesses to the root segment to be moved 64k higher to a section of flash starting at 20 bit address 64k that is reserved for constant data. A19 is normally inverted for data accesses to the data segment, causing the data accesses in the data segment to be moved to an address 512k higher in the 20 bit space, an address normally mapped to RAM. The stack segment and the XPC segment do

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Rabbit 3000 Microprocessor

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Jameco Electronics 2000, 3000 manual xpc window stack