Intel Microcontroller, 80C196NU manual Windowing, 8XC196NP

MEMORY PARTITIONS

5.3WINDOWING

Windowing expands the amount of memory that is accessible with direct addressing. Direct ad- dressing can access the lower register file with short, fast-executing instructions. With window- ing, direct addressing can also access the upper register file and peripheral SFRs.

Windowing maps a segment of higher memory (the upper register file or peripheral SFRs) into the lower register file. The 8XC196NP has a single window selection register, while the 80C196NU has two. The first, WSR, is the same in both devices. WSR selects a 32-, 64-, or 128- byte segment of higher memory to be windowed into the top of the lower register file space.

The second, WSR1, is unique to the 80C196NU. WSR1 selects a 32- or 64-byte segment of high- er memory to be windowed into the middle of the lower register file (Figure 5-4). Because the areas in the lower register file do not overlap, two windows can be in effect at the same time. For example, you can activate a 128-byte window using WSR and a 64-byte window using WSR1 (Figure 5-4). These two windows occupy locations 0040–00FFH in the lower register file, leav- ing locations 001A–003FH for use as general-purpose register RAM, locations 0018–0019H for the stack pointer or general-purpose register RAM, and locations 0000–0017H for the CPU SFRs.

128-byte Window

(WSR = 17H)

Window in

Lower Register File

8XC196NP

03FFH

0380H

037FH

0340H

00FFH

0080H

007FH

0040H

003FH

0000H

128-byte Window

(WSR = 17H)

64-byte Window (WSR1 = 2DH)

WSR Window in

Lower Register File

WSR1 Window in

Lower Register File

80C196NU

A3053-02

Figure 5-4. Windowing

5-13