For anyone wondering, X-ON and X-OFF are flow control characters. A device sends X-OFF to say "my buffer is full, stop sending data" and X-ON when it's ready to

For anyone wondering, X-ON and X-OFF are flow control characters. A device sends X-OFF to say "my buffer is full, stop sending data" and X-ON when it's ready to resume. On most Unix terminals, these have the effect of pausing and resuming the display when a bunch of data is scrolling by.