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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>DLC/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>DLC/E suspend<br />

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

clock.<br />

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

mode is exited as described above. While CLK2 is stopped, the <strong>TI486</strong>DLC/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 4-29. Stopping CLK2 During Suspend Mode<br />

CL~<br />

J-u-i:~r-KAAru-u-<br />

~ I I / (/J<br />

sUSP () {J () (J I () 'j-'<br />

----------~)(~)----------------~)(~J--~:--~)(~J--------~)(~J-------------<br />

10 CLK2s Min -......,1~4-----------.~1<br />

I<br />

)(~}------\~--------~)(~J----~)(~J--------~)(~J------i/<br />

4-53

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