ROM0:02B1 21 9B FF         ld hl,ff9b          // load counter offset to hl
ROM0:02B4 34               inc (hl)            // increment hl by 1(counter++)
ROM0:02B5 F0 04            ld a,(ff00+04)      // set a to the value at FF04
ROM0:02B7 47               ld b,a              // set b to it
ROM0:02B8 F0 E1            ld a,(ff00+e1)      // RNG byte 1 to a
ROM0:02BA 88               adc b               // add a and b(FF04 to FFE1)
ROM0:02BB E0 E1            ld (ff00+e1),a      // store the new a back to FFE1
ROM0:02BD F0 04            ld a,(ff00+04)      // set a to the value at FF04
ROM0:02BF 47               ld b,a              // set b to it
ROM0:02C0 F0 E2            ld a,(ff00+e2)      // RNG byte 2 to a
ROM0:02C2 98               sbc b               // subtract b from a(FF04 to FFE2)
ROM0:02C3 E0 E2            ld (ff00+e2),a      // store the new a back to FFE2