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I'm analyzing the following component:

http://www.futurlec.com/74HC/74HC574.shtml

It says that this flip-flop has a high impedance state when the output control bit is raised high. Does this allow the flip flop to be connected directly to a bus, without a buffer chip? If the chip is switched into high impedance mode would it lose the data locked into it?

I'm wanting to use this chip as a home brewed cpu register. I was looking at An octal buffer(54AC541) between this and the bus; however, I no longer think this is necessary.

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It appears from the data sheet that you should be able to connect it directly presuming you are using the output control pin in a manner that only one component connected to the bus can be selected at any one moment (it specifically states "Due to the large output drive capability and the 3-STATE feature, these devices are ideally suited for interfacing with bus lines in a bus organized system").

The flip flop does not lose data when you toggle the output enable pin.

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  • \$\begingroup\$ Thanks for the answer - I will certainly mark it. Do you know if data can be clocked in to storage while the output is set to high impedance? If not, then it wouldn't be able to read from the same bus that is connected as an output. Does this make sense? \$\endgroup\$
    – Dave C
    Dec 16, 2012 at 3:57
  • \$\begingroup\$ DaveC - yes, you can clock in the data while the output is turned off. The 574 is essentially a flipflop connected to a buffer with 3 state output. One of my devices uses 4 of these chips to store 32bits and then I can access it 8 bits at a time. And no, I do not have to enable the output to clock in new data. \$\endgroup\$
    – Pentium100
    Dec 16, 2012 at 4:03

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