User's Manual

CRXi

µµ

Core Module

µµ

X Logic,

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The flash area that contains the bootloader code consists of four 8K (2000h) segments and occupies the

80C320 code space at reset. It is automatically executed at reset regardless of the state of jumper J3. User

has no access to this code space and it is write protected. The bootloader’s main function is downloading

Intel .hex format files (users code), erasing the flash, reading and writing to memory and executing user

code. Other functions were incorporated into the boot code during development. Upon receiving the ‘G’

(go) command from the bootloader or reading the state of jumper J3 on reset, the bootloader code is

disabled and is overlayed with the users code and execution will again begin at address 0000h (80C320

reset vector).

The main flash gives the user access to 128K of code space. It consists of eight 16K (4000h) segments.

Since the 80C320 (and all 8051 derivatives) can address only 64K of code a paging scheme is used to

access the additional memory. If the users code is within the 64K limit the page register is of no concern to

the user. Flash segments 0 – 3 occupy the first 64K, called page 0, and this is the default page. There are

two additional pages for a total of three pages (page 0, page 1, page 2). Each page appears to have its own

64K space, but notice the bottom 32K of each page is duplicated in each page. This is referred to as the

common area and allows all pages to access a common area of code as well as all the interrupt vectors.

Figure 2 (CRXi memory map)

Switching between pages is done by writing to the page register, location C0E0h. The lower 2 bits are

written with 0, 1 or 2. The default is page 0 – no changes need be done if code occupies less than 64K

bytes. The user can use any paging scheme desired, being aware of the issues of paging. Many commercial

compilers

offer paging in their packages and is easily integrated. This is sometimes done by linking in a

special file into users code to handle the page switching and other details. Some modification of the paging

code may be needed.

NOTE: Care must be taken when writing to the page register. The upper bits of the page register are

reserved for internal use and must not be overwritten. Some commercial compiler vendors may not

protect unused bits in the page register – all writes to this register should be done via a mask to protect

these bits.