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Microcomputer Technical Q&A

Q&A No.: QAH8S-035

Category: Bus Controller

Subject: Program Wait Switchover Timing

Question

After a power-on reset, 3 program wait states are inserted in an external access cycle, making a 6-

state access. When external 3-state access is set, what is the switchover timing?

Answer

The switchover is made immediately after the wait control register (WCRH) is set. To set external

3-state access after a power-on reset, clear the Wn0 and Wn1 bits in WCR to 0.

An example of the switchover timing when waits are disabled by clearing all WCR bits to 0 with a

MOV instruction is shown below.

Example: MOV.W R1,@H'FED2:16

WCRH (address H'FED2), WCRL (address H'FED3) (assuming 0 is stored in R1)

3 states + 3 waits 3 states + 3 waits 2 states 3 states

R:W 2nd R:W NEXT W:W EA

MOV.W R1,@FED2:16

Address

HWR, LWR

1 2 ... 44 45 46 47 48 49 50 51 52 53 54 ... 147 148

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