Digi NS7520 manual Memory Space

Models: NS7520

1 332
Download 332 pages 47.95 Kb
Page 103
Image 103

M e m o r y C o n t r o l l e r M o d u l e

The BASE field in the Chip Select Base Address register defines the starting address of the chip select address space. The MASK field identifies those address bits, from A[31:12], that are used in the address decoding function.

A 1 in the MASK field indicates that the associated address bit is to be used in the decoding process.

A 0 in the MASK field indicates that the associated address is to be ignored in the address decoding process.

Note: When accessing a static memory device, the maximum value of the base address is 0x03000000.

To determine whether a BBus address is associated with a peripheral chip select, apply the following Boolean equation (chip select decode is TRUE when):

(({MASK,000} & 32-bit logical address) = = ({BASE,000} & {MASK,000}))

{MASK,000} is the MASK field concatenated with three nibbles of 0. {BASE,000} is the BASE field concatenated with three nibbles of 0.

&is the logical AND function.

==is the equal to operator.

The NS7520 supports only 28 address bits. Each chip select is limited to 256 Mbytes.

Memory Space

The MASK field can alias a memory location in different areas. The memory space associated with an individual chip select does not have to be continuous. Using the MASK field, you can set gaps in a single chip select range, essentially assigning the same chip select to different portions of the memory map.

Example

A 16 Mbyte device can be addressed in four different 64 Mbyte address locations by using a MASK value of ’hF3000. The peripheral is addressable at these address locations:

BASE + ’h00000000

BASE + ’h04000000

BASE + ’h08000000

BASE + ‘h0C000000

w w w . d i g i . c o m

8 9

Page 103
Image 103
Digi NS7520 manual Memory Space