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MSP430FR6989: number of rotary encoders with the Scan-IF interface of MSP430

Part Number: MSP430FR6989
Other Parts Discussed in Thread: MSP430FW428,

Just a questions to the Scan-IF interface of e.g. msp430fr6989 or msp430fw428. I am just in the beginning phase of a new project and have not used this interface before.

How many rotary encoders (quadrature enoding, I want to use magnetic encoders with a 3V TTL output, at max 85kHz, e.g. Bourns EMS22Q... ) can I connect to them? It is not really clear. It has 3 channels and only channel 2 can count up and downwards? I guess I can use it with just one encoder only?

A alternative would be software sampling of the two quadrature encoder channels within a timer interrupt. How fast can that be? Is 20kHz realistic? (I think it mainly depends on how long interrupts are blocked in the main code, in case I use code from e.g. TI libraries a interrupt blocking time is not really specified...).