Gravity comes from framesPerDropTable; a piece falls one row every 48 frames at level 0, never more slowly at a higher level, holding steady across levels 10–12, 13–15, and 16–18, down to 2 frames at levels 19–28, and 1 frame from level 29 on. | Dropping Tetriminos | Verified |
fallTimer counts frames, and when it reaches the level's value the piece moves down a row; if that row is blocked, the piece locks where it is, so a resting piece locks after one gravity interval. | Dropping Tetriminos | Code |
The first piece of a game hangs at the top for 96 frames before gravity starts, because autorepeatY starts at $A0 (−96) and gravity waits until it counts up to 0; pressing Down ends the wait. | Gamepad Version | Verified |
Holding Left or Right moves the piece at once, again 16 frames later, and then every 6 frames; the press zeroes autorepeatX, each held frame adds 1, and at DAS_RESET (16) the piece moves and the count drops to DAS_DELAY (10). | Shifting Tetriminos | Verified |
| A soft drop can't start while Left or Right is held. | Gamepad Version | Code |
Holding Down drops the piece a row on its 3rd frame and then every 2nd frame, and each piece needs a fresh press, because spawning zeroes autorepeatY and only a new press starts the count. | Gamepad Version | Code |
| The game has no hard drop; the only fast drop is the soft drop on Down. | Dropping Tetriminos | Web |
| Every new press of Left or Right zeroes the DAS count and moves the piece at once, so pressing on every other frame moves it every 2 frames. | Dropping Tetriminos | Verified |
The random number generator is a 16-bit linear feedback shift register at $0017; each step shifts it right and feeds bit 1 XOR bit 9 into the top bit, and from its seed, $8988, it repeats after 32,767 steps. | Picking Tetriminos | Verified |
| The NMI handler steps the generator every frame, so the time a player takes to place a piece changes which piece comes next. | Picking Tetriminos | Code |
pickRandomTetrimino adds a pick counter to the generator's high byte and keeps the low 3 bits; a result of 7, or the same piece as last time, makes it step the generator and take the high byte's low 3 bits plus the previous piece's orientation id, modulo 7, with no further check. | Picking Tetriminos | Code |
The reroll adds the previous piece's orientation id, not its index, so one of its eight results is doubled; after an O ($0A) or an S ($0B) the doubled result is the same piece again. | Picking Tetriminos | Code |
| In a long game the routine deals T and S most often (14.67% and 14.68%) and L and I least (13.89% each); J, Z, and O come 14.29–14.30% of the time. | Picking Tetriminos | Verified |
| The level first rises at 10 × (start level + 1) lines from start levels 0–9, at 100 lines from 10–15, and at 110, 120, 130, and 140 lines from 16, 17, 18, and 19; after that it rises every 10 lines. | Lines and Statistics | Verified |
Each time the lines' ones digit turns 0, the level goes up by 1 if it is below the hundreds and tens digits read as one hexadecimal byte; 130 lines gives $13, which is 19. | Lines and Statistics | Code |
| The NES draws 60.0988 frames per second. | Dropping Tetriminos | Web |
| Players call level 29 the "kill screen", although the game goes on. | The Kill Screen | Web |
| Engadget describes the level 29 kill screen as a wall for players who hold the D-pad, because DAS can't carry pieces to either edge in time. | Dropping Tetriminos | Magazine |
| Birken reports that the game itself breaks down around 1,550 lines, usually freezing, sometimes resetting or going black, because the scoring loop runs once per level and takes longer than a frame at high levels. | The Kill ScreenThe Kill Screen | Web |
| In competitive classic Tetris, holding the D-pad to move pieces is called DAS, for delayed auto shift. | Shifting Tetriminos | Magazine |
| Birken names Thor Aackerlund as a player who beat DAS at level 29 by vibrating the D-pad. | Dropping Tetriminos | Web |