Technical data

USB INITIALIZATION
DEVICE
40ms TIMER TICK ?
NEW ENDPOINT 1
YES
NEW ENDPOINT 2
USB IDLE FOR
YES
CONFIGURED ?
SCAN KEY MATRIX
YES
CONVERT SCAN KEY TO
KEYBOARD REPORT
REPORT ?
REPORT ?
6 ms ?
NO
EP1 TX BUFFER
YES
EMPTY ?
TX EP1 IN REPORT
YES
EP2 TX BUFFER
YES
EMPTY ?
TX EP2 IN REPORT
SUSPEND DEVICE
YES
KEY PRESSED OR
RESUME FROM
HOST ?
NO
NO
NO
YES
GHOST KEY?
NO
YES
USB and PS/2 Multimedia Keyboard Interface
USB and PS/2 Multimedia Keyboard Interface, Rev. 1
18 Freescale Semiconductor
Figure 1-11. USB Main Routine