Each IO can control 1 x LED, so the matrix shield can control 35-LED; Uses LED constant current control chip, can use SPI interface of Raspberry Pi(3 x IO+2), so it can control 64-LED.
It's a bit of troublesome to use LED lattice screen on Raspberry Pi due to the limited IO number of Raspberry Pi. If each IO controls one LED, then it can control 35 LED at most.
However, by utilizing constant current control chip made exclusively for LED, we can control 64 LED only by occupying SPI interface(three IO+ two enable ) of Raspberry Pi, thus turning LED lattice drive into reality.