Selecting A Window - Intel 8XC196K Series User Manual

Table of Contents

8XC196K x , J x , CA USER'S MANUAL

Windowing maps a segment of higher memory (the upper register file or peripheral SFRs) into

the lower register file. The window selection register (WSR) selects a 32-, 64-, or 128-byte seg-

ment of higher memory to be windowed into the top of the lower register file space. Figure 4-2

shows the upper register file of the 8XC196CA, JT, JV, KS, and KT devices. Please refer to Table

4-1 on page 4-2 for the upper register file addresses for other devices.

The 8XC196JV has additional register RAM in locations 1C00–1DFFH. Like the general-pur-

pose register RAM in the upper register file, this register RAM can be windowed and is accessed

directly, without the use of the memory controller.

Memory-mapped SFRs must be accessed using indirect or indexed addressing

modes; they cannot be windowed. Reading a memory-mapped SFR through a

window returns FFH (all ones). Writing to a memory-mapped SFR through a

window has no effect.

Selecting a Window

The window selection register (Figure 4-3) has two functions. The HLDEN bit (WSR.7) enables

and disables the bus-hold protocol (see Chapter 15, "Interfacing with External Memory"); it is

unrelated to windowing. The remaining bits select a window to be mapped into the top of the low-

er register file.

128-byte Window

Lower Register File

Figure 4-2. Windowing