SYSTEM CONFIGURATION

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.

external ROM area

MSM83C154S external ROM area

MSM80C154S

internal ROM area

 

MSM83C154S

65535 0FFFFH

16384 4000H

16383 3FFFH

44002CH

43002BH

0 7 6 5 4 3 2 1 0

Timer interrupt 2 start address

43

002BH

 

 

 

Serial I/O interrupt start address

 

0023H

35

Timer interrupt 1 start address

 

001BH

 

27

External interrupt 1 start address

 

0013H

 

19

Timer interrupt 0 start address

 

000BH

 

11

External interrupt 0 start address

 

0003H

 

3

 

 

 

 

2

0002H

 

 

 

 

1

0001H

 

 

 

CPU reset start address

0

0000H

 

 

 

Figure 2-24 MSM80C154S/MSM83C154S program area

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Sonic Alert msm80154s, msm83c154s user manual Program Memory and External Data Memory, 24 MSM80C154S/MSM83C154S program area