Weird SPI interface: VIH to VIHH for CS?

[mister_e]

I also have 10k resistors between the MCP4261 pins and the 16F628A pins, but that shouldn't affect anything.
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It still wasn't working... until I changed out the 10k resistors with 500 ohms.

Are you saying that your 10K resistor where in serie between the PIC and the MCP chip?

If so, you just don't need any, connect them directly. The only concern you may have, is the open-collector ones. In this case 10K or lower are nice between 5V and your pin.

[achilles03]

Are you saying that your 10K resistor where in serie between the PIC and the MCP chip?

If so, you just don't need any, connect them directly. The only concern you may have, is the open-collector ones. In this case 10K or lower are nice between 5V and your pin.

Yeah, I usually put them on to prevent burning out a pin on accident. What pins are considered "open-collector"? Do CS, CLK, and SI typically have internal resistors that limit current flow? What about SO?

Thanks!
Dave

[mister_e]

What you need to worry is your PIC I/O, some could be Open-Collector type, so if you use a open collector I/O as output, you need to add a pull-up resistor on it, unless your pin will never go to the high level unless your device have internal pull-up.

If you want to protect your PIC i/O from short, then use something like ~100-200 Ohm would work. In theory each I/O is capable to drive/sink 25mA... 5V/25mA=200 Ohms. Higher the current limiting + Faster your signal is, higher the chance to screw up your signal shape/edges/amplitude, higher the chance to have issue.


As you don't use Shiftin, you don't need to worry about SO