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SYSTEM CONFIGURATION
33
2.10 Program Memory and External Data Memory
2.10.1 MSM80C154S/MSM83C154S program area and external ROM connections
Since MSM80C154S/MSM83C154S are equipped with a 16-bit program counter, these
devices can execute programs of up to 64K bytes (including both internal and external
programs).
Since the MSM80C154S is not equipped with an internal program ROM, however, only
external instructions are executed. MSM83C154S, on the other hand, is equipped with a 16K
byte program ROM which enables it to execute internal instructions from address 0 thru
address 16383. External instructions are executed when the address is greater than 16383.
The program area is outlined in Figure 2-24, and a diagram of ROM connections made when
external instructions are executed is shown in Figure 2-25.
Timer interrupt 2 start address 43 002BH
Serial I/O interrupt start address 35 0023H
Timer interrupt 1 start address 27 001BH
External interrupt 1 start address 19 0013H
Timer interrupt 0 start address 11 000BH
External interrupt 0 start address 3 0003H
2 0002H
1 0001H
CPU reset start address 0 0000H76543210
002BH43
002CH44
3FFFH16383
4000H16384
0FFFFH65535
0
MSM80C154S external ROM area
MSM83C154S internal ROM area MSM83C154S external ROM area
Figure 2-24 MSM80C154S/MSM83C154S program area