ACI is a point-to-point, master-slave, and bi-directional serial bus. It has three features:
• The insertion and removal detection of an accessory device
• Acting as a data bus, intended mainly for control purposes
• The identification and authentication of accessory type which is connected The accessories are detected by the HeadInt signal when the plug is inserted.
Normally when no plug is present, the pull-up resistor 100k pulls up the HeadInt signal to VFLASH1. If the accessory is inserted, the external "insertion ft removal" resistor works as voltage divider and decrease the voltage level below the threshold Vhead.
Thereby the comparator output will be changed to high state causing an interrupt.
If the plug is removed, the voltage level of HeadInt increases again to VFLASH1. This voltage level is higher than the threshold of the comparator and thereby its output will be changed to low. This changes is leading to an interrupt.
These HeadInt interrupts are initiated the accessory detection or removal sequence.
If no accessory inserted / connected the only active part on the Pop-port interface is the ACI line.
ACI communication ©
Figure 18: ACI communication
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)
2a) If the phone detect a HeadInt interrupt from low to high transition in 20ms timeframe, then an advanced accessory is connected
3. ACI chip reset (3000- 4000us)
4. Power up delay (50-400us)
6 . Learning sequence (567-1700us)
7. ACI communication
8. MBUS is disconnected from HeadInt line (MBUS switch). After every communication.
9. Accessory is removed (no insertion ft removal resistor on ACI line) --> phone gets HeadInt interrupt from ACI line low to high transition.
9a) If no HeadInt interrupt comes in the next 100ms the accessory is really removed and the phone goes in the state "no accessory".
Table 18: Voltage Levels
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