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APPLICATION
7702/7703 Group User’s Manual
17–2
17.1 Memory expansion
This chapter describes application. Application shown here is just an example. The user shall modify them
according to the actual application and test them.
17.1 Memory expansion
This section shows examples for memory and I/O expansion. Refer to “Chapter 12. CONNECTION WITH
EXTERNAL DEVICES” for details about the functions and operation of used pins when expanding a memory
or I/O. Refer to “Chapter 15. ELECTRICAL CHARACTERISTICS” for timing requirements of the microcomputer.
Refer to “Chapter 18. LOW VOLTAGE VERSION” for timing requirements and application of the low
voltage version.
17.1.1 Memory expansion model
Memory expansion to the external is possible in the memory expansion mode or the microprocessor mode.
The level of the external data bus width select signal makes it possible to select the four memory expansion
models shown in Table 17.1.1.
(1)
Minimum model
This is an expansion model of which external data bus width is 8 bits and accessible area is
expanded up to 64 Kbytes. It is unnecessary to connect the address latch externally. This is an
expansion model having the cost priority which is suited for connecting the memory of which external
data bus width is 8 bits.
(2)
Medium model A
This is an expansion model of which external data bus width is 8 bits and accessible area is
expanded up to 16 Mbytes. In this expansion model, the high-order 8 bits of the external address bus
(A23 to A16) are multiplexed with the external data bus. Accordingly, an n-bit (n
≤ 8) address latch is
required for latching addresses (n bits of A23 to A16).
(3)
Medium model B
This is an expansion model of which external data bus width is 16 bits and accessible area is
expanded up to 64 Kbytes. This expansion model is used when having the speed performance
priority. In this expansion model, the middle-order 8 bits of the external address bus (A15 to A8) are
multiplexed with the external data bus. Accordingly, an 8-bit address latch is required for latching
address (A15 to A8).
(4)
Maximum model
This is an expansion model of which external data bus width is 16 bits and accessible area is
expanded up to 16 Mbytes. In this expansion model, the high- and middle-order 16 bits of the
external address bus (A23 to A8) are multiplexed with the external data bus. Accordingly, an 8-bit
address latch for latching A15 to A8 and an n-bit (n
≤ 8) address latch for latching n bits of A23 to A16
are required.