Information

At this point, control has been passed to system software via the interrupt. The rest of the
sequence (detecting the type of charging port) is not applicable, so software should:
1. Read the STATUS register.
2. Set CONTROL[IACK] to acknowledge the interrupt.
3. Set CONTROL[SR] to issue a software reset to the module.
4. Disable the module.
41.5.1.5 Charger type detection
After software enables the D+ pullup resistor, the module is notified automatically (via
internal signaling) to start the CHECK_DM timer counting down the time interval
programmed in the TIMER2[CHECK_DM] field.
After the CHECK_DM time has elapsed, the module samples the USB D– line to
determine the type of charger. See the following table.
Table 41-17. Sampling D– in the charger type detection phase
If the voltage on D– is... Then... See...
High The port is a dedicated charging port.
1
Dedicated
charging port
Low The port is a charging host port.
2
Charging host
port
1. In a dedicated charger, the D+ and D– lines are shorted together through a small resistor.
2. In a charging host port, the D+ and D– lines are not shorted.
41.5.1.5.1 Dedicated charging port
For a dedicated charger, the module does the following:
• Updates the STATUS register to reflect that a dedicated charger has been detected
with SEQ_RES = 11. See Table 41-18 for field values.
• Sets CONTROL[IF].
• Generates an interrupt if enabled in CONTROL[IE] bit.
At this point, control has been passed to system software via the interrupt. Software
should:
1. Read the STATUS register.
Chapter 41 USB Device Charger Detection Module (USBDCD)
K20 Sub-Family Reference Manual, Rev. 2, Feb 2012
Freescale Semiconductor, Inc. 945