Figure 19: Signal flow on ACI Line

1. Accessory is connected (insertion ft removal resistor connect to ACI line)

1a) phone gets HeadInt interrupt after 20ms check that ACI line is still low (<Vhead min)

2. Connect MBUS with HeadInt line (MBUS switch)

3. The 20 ms timer elapsed and no transition has been on HeadInt line 3a) Disconnect MBUS from HeadInt line

4. Accessory is removed. Phone gets HeadInt interrupt from ACI line low to high transition

4a) If no HeadInt interrupt comes in the next 100ms the accessory is really removed.

FBUS is an asynchronous data bus with separate TX and RX signals. Default bit rate of the bus is 115 . 2 Kbit/s.

FBUS is used as additional communication channel from phone to accessory and vice versa. There is two types of accessories which it uses:

1. Nokia Serial Bus Accessory, AT mode

2. Fbus Phonet mode accessory

From HW-point of view, this does not make any difference .

Table 19: FBUS interface









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