[ATN]    asserted -> DATA low (ack)
[ATN]    released -> not addressed -> IDLE
[IDLE]   waiting for ATN
[ATN]    asserted -> DATA low (ack)
[ATN]    released -> not addressed -> IDLE
[IDLE]   waiting for ATN
[ATN]    asserted -> DATA low (ack)
[ATN]    released -> not addressed -> IDLE
[IDLE]   waiting for ATN
[ATN]    asserted -> DATA low (ack)
[ATN]    released -> not addressed -> IDLE
[IDLE]   waiting for ATN