Introduction to the HCS12 Microcontroller - The HCS12/9S12: An Introduction to Software and Hardware Interfacing - page 17

Program memory
address bus

75
20
00
75
21
14
90
20
00

0x0000

CPU

E0

54
03

70
02
05
20
D5
21
0A

Before read

0x75

0x0000

Program memory
data bus

PC

After read

0x0001

PC

Figure 1.5 ■ Instruction 1-opcode read cycle

Data memory

Data memory
address bus

xx
xx
xx
xx
xx
xx
xx
xx
xx

0x20

CPU

xx

xx
xx

Before write

0x0003

xx
xx
xx
xx

0x00

PC

After write

Data memory
data bus

0x0003

xx

PC

Figure 1.6 ■ Instruction 1-data memory write cycle