Sonic Alert msm83c154s, msm80154s, msm85c154hvs user manual Program Counter, CPU Internal Data BUS

Models: msm83c154s msm85c154hvs msm80154s

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MSM80C154S/83C154S/85C154HVS

2.9 Program Counter

The MSM80C154S/MSM83C154S program counter has a 16-bit configuration PC0 thru PC15, as shown in Figure 2-23.

INTERNALCPU BUSDATA

EXTERNAL

ROM MODE

ENABLE ROM

MSM83C154S INTERNAL ROM 16KWORD 8BIT

Q15 Q14 Q13 Q12 Q11 Q10 Q9 Q8

Q7

Q6

Q5

Q4

Q3

Q2

Q1

Q0

PC+1

D15 D14 D13 D12 D11 D10 D9 D8

D7

D6

D5

D4

D3

D2

D1

D0

CPU INTERNAL DATA BUS

Figure 2-23 MSM80C154S/MSM83C154S program ounter

This program counter is a binary up-counter which is incremented by 1 each time one byte of instruction code is fetched. When the program counter is counted by 1 after counter contents have reached 0FFFFH, the counter is returned to 0000H. MSM83C154S is automatically switched to external ROM mode when the counter contents exceed 3FFFH.

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Sonic Alert msm83c154s, msm80154s, msm85c154hvs user manual Program Counter, CPU Internal Data BUS