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MSM80C154S/83C154S/85C154HVS
32
2.9 Program Counter
The MSM80C154S/MSM83C154S program counter has a 16-bit configuration PC0 thru
PC15, as shown in Figure 2-23.
Q8Q9Q10Q11Q12Q13Q14Q15
D8D9D10D11D12D13D14D15
Q0Q1Q2Q3Q4Q5Q6Q7
D0D1D2D3D4D5D6D7
PC+1
MSM83C154S INTERNAL ROM
16KWORD × 8BIT
CPU INTERNAL
DATA BUS
EXTERNAL
ROM MODE
ENABLE ROM
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.