MC68HC11K0CFN3 MOTOROLA [Motorola, Inc], MC68HC11K0CFN3 Datasheet - Page 35

• Manufacturer Part Number: MC68HC11K0CFN3
• Description: Technical Summary 8-Bit Microcontroller
• Manufacturer: MOTOROLA [Motorola, Inc]

Bit 7 — Not implemented
G2DPC — General-Purpose Chip Select 2 Drives Program Chip Select
G2POL — General-Purpose Chip Select 2 Polarity Select
G2AV — General-Purpose Chip Select 2 Address Valid Select
G2SZA–G2SZD — General-Purpose Chip Select 2 Size
4.3.6 Examples of Memory Expansion Using Chip Selects
M68HC11 K Series
MC68HC11KTS/D
Always reads zero
On the following two pages are examples of memory expansion schemes that use chip select signals
to simplify the interface to the external memory devices. Although schematics are not provided, careful
study of the memory map diagram for each example will reveal the simplicity with which an expanded
system can be created. Both examples require a minimum of external circuitry as well as very little pro-
gram code.
This example is a system consisting of the MCU and a single 27C512-type memory device. This system
uses one chip select and has one window containing eight banks of eight Kbytes each. In this example,
a total of 64 Kbytes is added to the address range of the MCU. Three of the expansion address lines
(XA[15:13]) are used. Register values particular to this example are given below the diagram.
A
0
0
0
0
0
0
0
0
1
1
1
1
0 = CSGP2 does not affect CSPROG
1 = CSGP2 and CSPROG are connected to an OR gate and driven out CSPROG
0 = CSGP2 active low
1 = CSGP2 active high
0 = Active during E high time
1 = Active during address valid time
B
0
0
0
0
1
1
1
1
0
0
0
0
1100–1111
G2SZx
C
0
0
1
1
0
0
1
1
0
0
1
1
D
0
1
0
1
0
1
0
1
0
1
0
1
Follow Window 1
Follow Window 2
Default to 512 K
Size (Bytes)
Disabled
128 K
256 K
512 K
16 K
32 K
64 K
2 K
4 K
8 K
(MXGS2 = 0)
ADDR[15:11]
ADDR[15:12]
ADDR[15:13]
ADDR[15:14]
Valid Bits
ADDR15
None
None
None
None
None
None
None
None
(MXGS2 = 1)
G2A[18:11]
G2A[18:12]
G2A[18:13]
G2A[18:14]
G2A[18:15]
G2A[18:16]
G2A[18:17]
Valid Bits
G2A18
None
None
None
None
None
MOTOROLA
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