MC68HC711K4CFN4 Datasheet, PDF (35/80 Pages) Motorola, Inc – 8-Bit Microcontroller

Bit 7 — Not implemented
Always reads zero
G2DPC — General-Purpose Chip Select 2 Drives Program Chip Select
0 = CSGP2 does not affect CSPROG
1 = CSGP2 and CSPROG are connected to an OR gate and driven out CSPROG
G2POL — General-Purpose Chip Select 2 Polarity Select
0 = CSGP2 active low
1 = CSGP2 active high
G2AV — General-Purpose Chip Select 2 Address Valid Select
0 = Active during E high time
1 = Active during address valid time
G2SZA–G2SZD — General-Purpose Chip Select 2 Size
G2SZx
Valid Bits
Valid Bits
A
B
C
D
Size (Bytes)
(MXGS2 = 0)
(MXGS2 = 1)
0
0
0
0
Disabled
None
None
0
0
0
1
2K
ADDR[15:11]
G2A[18:11]
0
0
1
0
4K
ADDR[15:12]
G2A[18:12]
0
0
1
1
8K
ADDR[15:13]
G2A[18:13]
0
1
0
0
16 K
ADDR[15:14]
G2A[18:14]
0
1
0
1
32 K
ADDR15
G2A[18:15]
0
1
1
0
64 K
None
G2A[18:16]
0
1
1
1
128 K
None
G2A[18:17]
1
0
0
0
256 K
None
G2A18
1
0
0
1
512 K
None
None
1
0
1
0
Follow Window 1
None
None
1
0
1
1
Follow Window 2
None
None
1100–1111
Default to 512 K
None
None
4.3.6 Examples of Memory Expansion Using Chip Selects
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.
M68HC11 K Series
MC68HC11KTS/D
MOTOROLA
35