Texas Instruments MSC1210 - Manual (Page 23)

MSC1210 Pin-Out
1-11
Introduction to the MSC1210
1.2.6 External Access (EA)
The external access (EA) line at pin 48 is used to determine whether the
MSC1210 will execute your program from external code memory or from inter-
nal code memory. If EA is tied high (connected to supply), the microcontroller
will execute the program it finds in internal/on-chip code memory. If EA is tied
low (to ground), it will attempt to execute the program that it finds in the at-
tached external program memory. Of course, the external program memory
must be properly connected for the microcontroller to be able to access the
program in external program memory.
The EA pin is ignored during serial or parallel flash programming modes.
Note:
Even when EA is tied high (indicating that the microcontroller should execute
from internal code memory), the microcontroller will attempt to execute from
external code memory if the program counter references an address not
available for the chip you are using, or if you are accessing program memory
in excess of the amount of flash memory that you have partitioned for pro-
gram memory. For example, if you have partitioned 4k of flash memory to be
program memory and you tie EA high, the derivative starts executing the pro-
gram it finds on-chip. However, if your on-chip program attempts to execute
code above 0FFF
H
(that is, exceeding 4k), then the MSC1210 will attempt
to execute that code at that address from external code memory. Thus, it is
possible to have a split design, in which some of the code is found on-chip
and the rest is found off-chip.