Windowing And Addressing Modes - Intel 8XC196NT User Manual

8XC196NT USER'S MANUAL
This listing shows the disassembled code:
2080H ;C814
2082H ;B14814
2085H ;44E4E2E0
2089H ;B21814
208CH ;65020018
2090H ;F0
2091H ;C814
2093H ;B14814
2096H ;44EAE8E6
209AH ;B21814
209DH ;65020018
20A1H ;F0
The C compiler can also take advantage of this feature if the "windows" switch is enabled. For
details, see the MCS 96 microcontroller architecture software products in the Development Tools
Handbook.
4.3.3

Windowing and Addressing Modes

Once windowing is enabled, the windowed locations can be accessed both through the window
using direct addressing and through its actual address using indirect or indexed addressing. The
lower register file locations that are covered by the window are always accessible by indirect or
indexed operations. To re-enable direct access to the entire lower register file, clear the WSR. To
enable direct access to a particular location in the lower register file, you may select a smaller
window that does not cover that location.
When windowing is enabled:
•
a direct instruction that uses an address within the lower register file actually accesses the
window in the upper register file;
•
an indirect or indexed instruction that uses an address within either the lower register file or
the upper register file accesses the actual location in memory.
The following sample code illustrates the difference between direct and indexed addressing when
using windowing.
PUSHA
LDB WSR, #12H
ADD 40H, 80H
ADD 40H, 80H[0]
ADD 40H, 380H[0]
POPA
4-22
| PUSH WSR
| LDB WSR,#48H
| ADD E0H,E2H,E4H
| LDB WSR,[SP]
| ADD SP,#02H
| RET
| PUSH WSR
| LDB WSR,#48H
| ADD E6H,E8H,EAH
| LDB WSR,[SP]
| ADD SP,#02H
| RET
; pushes the contents of WSR onto the stack
; select window 12H, a 128-byte block
; The next instruction uses direct addr
; mem_word(40H)←mem_word(40H) + mem_word(380H)
; The next two instructions use indirect addr
; mem_word(40H)←mem_word(40H) + mem_word(80H +0)
; mem_word(40H)←mem_word(40H) + mem_word(380H +0)
; reloads the previous contents into WSR