Is the 74HC4094 SPI compatible?

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Hey Freaks,

Is it possible to use the 74HC4094 shift register on an SPI bus? It doesn't specifically say you can in the datasheet. If I tie OE to Vcc, can I use the strobe as a chip select?

Thanks
Dave.

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It is possible, I would suggest to be carefull though.. If you use the SPI pins for other stuff, or if you use the ISP, you may find some garbage comming out of that chip.

an object at rest...
cannot be stopped!

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daveavr wrote:
Hey Freaks,

Is it possible to use the 74HC4094 shift register on an SPI bus? It doesn't specifically say you can in the datasheet. If I tie OE to Vcc, can I use the strobe as a chip select?

Thanks
Dave.

I'd use the 74HC595, that is definitely SPI-compatible. I use one on a little PCB with LEDs on the outputs for debugging SPI software.

Leon

Leon Heller G1HSM

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Yes, I've used it like that. Also used more than one. There are two ways to connect more than one shift register. You can connect the data and clock of each together to the SPI port and use separate port pins for the strobe signal for each shift register. Need to clock 8 bits out and then strobe the appropriate shift register. The other way is to connect the QS2 output to the D input of the next one. In this case the strobe signals of all the shift registers connect together as well. Now need to clock n * 8 bits out before strobing.

Arthur

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if the shift registers are sharing the same miso pin as the rest of your SPI perhaprial's then it might need to be gated together with the clk using a 74HCT125 or similar circuit, using the shiftregister CS as a gate. this is to have a high-impedence output from the shift registers, allowing other perhaprial to drive this line. the clock might need to be gated unless the shift registers can handle clock cycles given to them while in inactive state (dependant of what shift registers you use, and how you control them).

Best regards:
Magnus