How much current is involved in SPI transmition?

Hello! Best regards From Chile.

I Would like to ask about SPI protocol. Hope you can help me.

Well, I'm working on a MIDI controller... I'm using a Arduinos main uC to control 4 cascade 74hc595 shift register's using SPI to manage a 7segment display and some RGB leds so the user can know if it is on preset A from bank 1, 2 or 3. (I'm taking care of the current draw to not exceed the 595 limit)

The main concern is about the UC SPI lines... MOSI, MISO and SCK... Do I need to buffer them? how much current is being involved on SPI lines?

The buffers that are available on my country can only source 8mA. Should this be enough to drive the SPI lines to the 4 shift registers?

I hope I have made myself clear!

Thanks so much for your help and knowledge. Stay safe!

The 74HC595 inputs are high impedance, low capacitance. You do not need to worry about buffers between the Arduino pins and the 74HC595 inputs.

No need to use SPI to send the data. Use your favorite search engine to find tutorials.

They are logic signals, so the driving abiliity (aka fanout) depends on the logic family or families involved. With CMOS the static current drain is zero, its the capacitance that usually limits fanout by causing edges to become too slow for reliable operation.

For CMOS I'd not even worry about unless you want a fanout of 10 or more.