4.a. ATmega168's Attention Line
Whenever a bit gets set in the mega168’s status byte, the mega168 sets its attention line. Whenever a Get Status command (218—Section 3.d.01) is issued, the mega168 clears the attention line. In the Orangutan X2’s default configuration, the attention line is not connected to the mega644 and hence any status changes must be detected via polling the status byte with Get Status commands. If desired, you can connect the attention line to one of the mega644’s IO pins. Whenever this pin goes high, you know to send a Get Status command. Connecting the attention line to the mega644 gives you a simpler polling method, and it also gives you the option to trigger an interrupt every time a status bit is set. You can access the attention line via the through-hole labelled ATT on the back of the main board. It is located near the center of the board. The attention line is a purely optional feature.