Player Y speed (8-bit, 2-complement signed), in 1/16s of a pixel per frame:
$80-$FF: Upwards speed, with $80 being the fastest (launches the player the highest)
$00: Not moving vertically.
$01-$7F: Downwards speed, with $7F being the fastest.
Note: $43 (when holding jump) $46 (not holding jump) is the maximum fall speed. Although $40 is the intended max speed (see at $00D7AF), the code first caps the downwards speed, and then apply the gravitational acceleration (increases Y speed by $03 or $06) afterwards.
When jumping, $B3 is the normal jump speed, and #$A4 is the jump speed when fully running.