MC68HC11KW1 Datasheet, PDF (79/238 Pages) Motorola, Inc – High-density complementary metal oxide semiconductor HCMOS) microcontroller unit

4.5.5 General-purpose chip selects
The general-purpose chip selects are the most flexible and programmable and have the most
control bits. Polarity of active state, E valid or address valid, size, and starting address are all
programmable. Clock stretching can be set from zero to three cycles.
Each general-purpose chip select has two registers. One, the control register GPCSxC,
determines the logical output required when an area of memory is selected and the range of
memory over which the chip select is to be active. Each chip select can be programmed to become
active whenever the CPU address enters a memory expansion window, regardless of the actual
4
bank selected. This is known as following a window.
The second, the address register GPCSxA, allows the starting address of the chip select to be
programmed. The bits in this register that are valid are determined by the size of the chip select
range selected by the control register.
Refer to the descriptions of the two associated registers for starting address and control
information.
In cases where one general-purpose chip select is programmed to drive the other
general-purpose chip select or the program chip select, determine the priority from Table 4-14.
Table 4-14 General purpose chip select priority
Condition
GPCS1 drives GPCS2
GPCS1 drives PCS
GPCS2 drives PCS
GPCS1 and GPCS2 drive PCS
Priority
GPCS1
GPCS1
GPCS2
GPCS1
4.5.5.1 GPCS1A — General-purpose chip select 1 address register
Address bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
State
on reset
Gen. purpose chip select 1 addr. (GPCS1A) $005C G1A18 G1A17 G1A16 G1A15 G1A14 G1A13 G1A12 G1A11 0000 0000
G1A[18:11] — General-purpose chip select 1 address
These bits select the starting address of general-purpose chip select 1 range. Refer to Table 4-15.
MC68HC11KW1
OPERATING MODES AND ON-CHIP MEMORY
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