HCS12 Assembly Programming - The HCS12/9S12: An Introduction to Software and Hardware Interfacing - page 82

Example 2.25
▼

Write an instruction sequence to create a 100-ms time delay for a demo board with a
24-MHz bus clock.
Solution: In order to create a 100-ms time delay, we need to repeat the preceding instruction
sequence 60,000 times [100 ms ÷ (40 ÷ 24,000,000)

μ s 5 60,000]. The following instruction

sequence will create the desired delay:

ldx #60000 ; 2 E cycles

loop psha ; 2 E cycles

pula ; 3 E cycles

psha ; 2 E cycles

pula ; 3 E cycles

psha ; 2 E cycles

pula ; 3 E cycles

psha ; 2 E cycles

pula ; 3 E cycles

psha ; 2 E cycles

pula ; 3 E cycles

psha ; 2 E cycles

pula ; 3 E cycles

psha ; 2 E cycles

pula ; 3 E cycles

nop ; 1 E cycle

nop ; 1 E cycle

dbne x,loop ; 3 E cycles

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Example 2.26
▼

Write an instruction sequence to create a delay of 10 sec.
Solution: The instruction sequence in Example 2.25 can only create a delay slightly longer than
100 ms. In order to create a longer time delay, we need to use a two-layer loop. For example, the
following instruction sequence will create a 10-sec delay:

ldab #100 ; 1 E cycle

out_loop ldx #60000 ; 2 E cycles

inner_loop psha

pula

psha

pula

psha

pula

psha

pula

psha

pula

psha

pula