SN74HC165: GPIO extension for microcontroller in combination with the SN74HC595

Markus Nabecker

Part Number: SN74HC165
Other Parts Discussed in Thread: SN74HC595, CD74HC299, SN74LVC1G04, SN74AHC1G04

Dear support team,

I am currently working at an GPIO extension for a microcontroller. I want to use 1 SPI Port for the extension with digital inputs and outputs.

I have created a first draft version of the schematic and want to ask if it is possible to combine these two extension ICs together.

Could you please check if this could work?

0 Clemens Ladisch over 1 year ago

Guru 268120 points

It is possible to connect both to the same SPI clock (SHIFT_CLK).

However, the '595 requires SPI mode 0 or 3. The '165 requires SPI mode 2. You cannot access them in the same transaction.

The connection from the Q_H' output of the '595 to the SER input of the '165 is not necessary (and cannot work due to the different SPI modes).

0 Markus Nabecker over 1 year ago in reply to Clemens Ladisch

Does TI has another GPIO-extension IC in his portforlio were I can use them in this way?

+1 Clemens Ladisch over 1 year ago in reply to Markus Nabecker

Guru 268120 points

No. (The CD74HC299 can be cascaded and has both input and output modes, but is not SPI compatible.)

But you can add an inverter (e.g., SN74AHC1G04/SN74LVC1G04) in front of the '165's clock input so that all work in SPI mode 0.

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