Action: Returns relative mouse motion and button data (added in FLOS v571)

Input Registers : none

Output Registers :

• HL = relative x motion since last called
• DE = relative y motion since last called
• A = buttons status
• Zero Flag: if not set, the mouse driver has not been enabled

(Note: the mouse driver is currently somewhat primative - it may become out of sync with the three-byte packets that the mouse sends if for example, interrupts are disabled)