7643 datasheet(308/424 Pages) RENESAS

308 / 424 page

Rev.2.00

Aug 28, 2006

page 187 of 202

7643 Group

REJ09B0133-0200

APPLICATION

2.8 External device connection

(4) RDY function

When using RDY function in usual connection, it does not operate at 12 MHz of

φ or faster.

[Reason]

td(

φ-AH) + tsu(RDY-φ) = 31 ns (max.) + 21 ns (min.) = 52 ns.

twh (

φ), twl (φ) = 0.5 ✕ 83.33 – 5 = 36.665 ns

Therefore, it becomes 52 ns > 36.665 ns, so that the timing to enter RDY wait does not match.

________

However, if the timings can match owing to RDY pin by “L” fixation and others, the RDY function

can be used even at

φ = 12 MHz. In this situation the slow memory wait always functions.

(5) Wait function

The Wait function is serviceable at accessing an external memory in the memory expansion mode

and microprocessor mode. However, in these modes even if an external memory is assigned to

addresses 000816 to 000F16, the Wait function cannot function to these areas.

(6) Processor mode switch

Note when the processor mode is switched by setting of the processor mode bits (b1, b0 of

CPMA), that will immediately switch the accessible memory from external to internal or from

internal to external. If this is done, the first cycle of the next instruction will be operated from the

accidental memory.

To prevent this problem, follow the procedure below:

(a) Duplicate the next instruction at the same address both in internal and external memories.

(b) Switch from single-chip mode to memory expansion mode, jump to external memory, and then

switch from memory expansion mode to microprocessor mode. (Because in general, the problem

will not occur when switching the modes as long as the same memory is accessed after the

switch.

program, then jump to the location of the code to run after the processor mode has switched.

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