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Data Memory
2-5
MSC1210 Memory Organization
On-chip extended static RAM provides 1k of data memory that requires no ex-
ternal circuitry and is available regardless of how the MSC1210’s flash
memory is designated. This makes it a convenient memory area for purposes
such as temporary buffers, calculation scratchpads, or any other purpose that
requires 1k or less of memory, but does not require it to survive a power failure.
2.3.2 On-Chip Flash Data Memory
In addition to the on-chip extended SRAM described in the previous section,
the MSC1210 also has the capability of offering on-chip flash data memory.
Flash memory is slower than SRAM, but has the advantage of being nonvola-
tile: its contents will not be lost when the power source is removed.
All of the parts in the MSC1210 family come with some amount of on-chip flash
memory, ranging from 4k for the MSC1210Y2 all the way up to 32k for the
MSC1210Y5. This flash memory may be configured such that it can be used
as either program memory, data memory, or both.
When configured as data memory, on-chip flash data memory is accessed
starting at address 0400
H
—immediately after on-chip SRAM.
For example, if the MSC1210Y5 is configured to use 2k as on-chip flash data
memory, addresses 0000
H
through 03FF
H
will access on-chip extended SRAM
while addresses 0400
H
through 0BFF
H
will access on-chip flash data memory.
Any attempts to read data memory with addresses 0C00
H
and higher will result
in the part attempting to fetch that data off-chip from external data memory (see
the next section), except when the internal 1kB SRAM is configured as Von Neu-
mann type, which occupies from 8400
H
∼87FF
H
.
2.3.3 External Data Memory
The MSC1210 is capable of addressing up to 64k of data memory, however,
a maximum of 33k of that may be on-chip: 1k of SRAM and up to 32k of flash
data memory. If additional data memory is necessary, it must be added to the
circuit as external data memory.
External data memory is any off-chip data memory that is connected to the
MSC1210 via ports 0 and 2 and uses control pins ALE, RD
, and WR. These
two ports combined with these three control lines allow the MSC1210 to ad-
dress external RAM.
External data memory can also be used to access “memory mapped devices,”
which are devices that appear to the MSC1210 to be external data memory
but in reality are external components such as LCDs, buttons, keypads, etc.
Note:
The MSC1210 must only address 64kB of RAM. To expand RAM beyond this
limit requires programming and hardware tricks. It may be necessary to do this
“by hand” because many compilers and assemblers, while providing support for
programmers in excess of 64kB, do not support more than 64kB of RAM. If more
than 64kB of RAM is necessary, the compiler must be checked to verify that the
excess RAM is supported. If not, it will be necessary to do it “by hand.”