 Adafruit_TrellisSet trellis(&T[0], &T[1], &T[2], &T[3]);
 const uint8_t       addr[] = { 0x70, 0x71, 0x72, 0x73 };
 
-boolean       grid[8][8];                  // Sequencer state
+uint8_t       grid[8];                     // Sequencer state
 uint8_t       heart        = 0,            // Heartbeat LED counter
               col          = 0;            // Current column
 unsigned int  bpm          = 240;          // Tempo

        uint8_t xy = pgm_read_byte(&i2xy[i]),
                x  = xy >> 4,
                y  = xy & 0x0F;
        if(trellis.justPressed(i)) {
          if(grid[x][y]) { // Already set?  Turn off...
            grid[x][y] = false;
            trellis.clrLED(i);
            usbMIDI.sendNoteOff(pgm_read_byte(&note[y]),
              127, pgm_read_byte(&channel[y]));
          } else {         // Turn on
            grid[x][y] = true;
            trellis.setLED(i);
          }
          refresh = true;

    { 17, 21, 25, 29, 49, 53, 57, 61 },
    { 18, 22, 26, 30, 50, 54, 58, 62 },
    { 19, 23, 27, 31, 51, 55, 59, 63 } },
  note[8]    = {  72, 71, 69, 67, 65, 64, 62, 60 },
  channel[8] = {   1,  1,  1,  1,  1,  1,  1,  1 },
  bitmask[8] = { 128, 64, 32, 16,  8,  4,  2,  1 };

void setup() {
  pinMode(LED, OUTPUT);
