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CENTRAL PROCESSING UNIT (CPU)

7733 Group User’s Manual

2–28

2.5.3 Selection of processor mode

A processor mode can be selected by setting a voltage applied to pin CNVSS and the processor mode bits

(bits 1 and 0 at address 5E16).

q When VSS level is applied to pin CNVSS

After reset, the microcomputer starts operating in the single-chip mode. After the microcomputer starts

operating, the processor mode can be switched by the processor mode bits. When the contents of the

processor mode bits = “012,” the memory expansion mode is selected; when the contents of these bits

= “102,” the microprocessor mode is selected. After the processor mode bits are set, the processor

mode is actually switched at the rising edge of signal E. Figure 2.5.3 shows the pin function switch

timing when the processor mode is switched from the single-chip mode to the memory expansion or

microprocessor mode by setting the processor mode bits. Note that, when the processor mode is

switched during the program execution, the contents of the instruction queue buffer is not initialized.

(Refer to section “Appendix 9. Q & A.”)

q When VCC level is applied to pin CNVSS

After reset, the microcomputer starts operating in the microprocessor mode. In this case, the microcomputer

cannot operate in the other modes. (Fix the processor mode bits to “102.”)

Table 2.5.2 lists the method of selecting the processor mode. Figure 2.5.4 shows the structure of the

processor mode register 0.

P07

External address bus A7

Writing to the processor mode bits

Programmable I/O port P07

Note: Functions of pins P00 to P06, P1 to P3, P40 to P42 are switched at the timing shown above.

Function of pin P42 is, however, switched only when the processor mode is switched to

microprocessor mode.

Fig. 2.5.3 Pin function switch timing

2.5 Processor modes

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