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TI486 Microprocessor - Al Kossow's Bitsavers

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Functional Timing<br />

Stopping the Input Clock<br />

Because the <strong>TI486</strong>SLC/E is a static device, the input clock (CLK2) can be<br />

stopped and restarted without loss of any internal CPU data. CLK2 can be<br />

stopped in either phase 1 or phase 2 of the clock and in either a logic high or<br />

logic low state. However, entering suspend mode prior to stopping CLK2<br />

dramatically reduces the CPU current requirements. Therefore, the<br />

recommended sequence for stopping CLK2 is to initiate <strong>TI486</strong>SLC/E suspend<br />

mode, wait for assertion of SUSPA by the processor and then stop the input<br />

clock.<br />

The <strong>TI486</strong>SLC/E remains suspended until CLK2 is restarted and suspend<br />

mode is exited as described above. While CLK2 is stopped, the <strong>TI486</strong>SLC/E<br />

can no longer sample and respond to any input stimulus including the HOLD,<br />

FLUSH, NMI, INTR and RESET inputs. Figure 3-26 illustrates the<br />

recommended sequence for stopping CLK2 using SUSP to initiate suspend<br />

mode. CLK2 should be stable for a minimum of 10 clock periods before SUSP<br />

is deasserted.<br />

Figure 3-26. Stopping CLK2 During Suspend Mode<br />

CL~<br />

J-u-i:~r-KAAJ-u-U-<br />

~ I J<br />

suSP<br />

_<br />

\ ') (, ') " I ')'j-'<br />

________ ~((~----------------~(( I<br />

'/,<br />

}}- J) I )(.,..,--------~)(.,..J-------------<br />

10 CLK2s Min ----1IIe~-------------.,.1<br />

I<br />

--------~)'~'-----\~ ________ ~)'~,----~)~)--------~)(~j ____ J!I<br />

3-46 <strong>TI486</strong>SLCIE Bus Interface

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