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8XC196NP, 80C196NU USER’S MANUAL
5-14
5.3.1 Selecting a Window
The window selection register (Figure 5-5) has two functions. The HLDEN bit (WSR.7) enables
and disables the bus-hold protocol (see Chapter 13, “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. Window selection register 1 (Figure 5-6) selects a second window to be mapped
into the middle of the 80C196NU’s lower register file.
Table 5-8 provides a quick reference of WSR values for windowing the peripheral SFRs. Table
5-9 on page 5-15 lists the WSR values for windowing the upper register file.
WSR
Address:
Reset State:
0014H
00H
The window selection register (WSR) has two functions. One bit enables and disables the bus-hold
protocol. The remaining bits select windows. Windows map sections of RAM into the top of the lower
register file, in 32-, 64-, or 128-byte increments. PUSHA saves this register on the stack and POPA
restores it.
7 0
HLDEN W6 W5 W4 W3 W2 W1 W0
Bit
Number
Bit
Mnemonic
Function
7 HLDEN HOLD#, HLDA# Protocol Enable
This bit enables and disables the bus-hold protocol (see Chapter 13,
“Interfacing with External Memory”). It has no effect on windowing.
1 = enable
0 = disable
6:0 W6:0 Window Selection
These bits specify the window size and window number. See Table 5-8
on page 5-15 or Table 5-9 on page 5-15.
Figure 5-5. Window Selection (WSR) Register