Information

USBDCD_TIMER2 field descriptions (continued)
Field Description
25–16
TVDPSRC_CON
Time Period Before Enabling D+ Pullup
Sets the amount of time (in ms) that the module waits after charging port detection before system
software should enable the D+ pullup to connect to the USB host. Valid values are 1-1023, but the USB
Battery Charging Specification requires a minimum value of 40 ms.
15–4
Reserved
This read-only field is reserved and always has the value zero.
3–0
CHECK_DM
Time Before Check of D- Line
Sets the amount of time (in ms) that the module waits after the device connects to the USB bus (software
enables the D+ pullup) until checking the state of the D- line to determine the type of charging port. Valid
values are 1-15ms.
43.5 Functional Description
The sequence of detecting the presence of and type of charging port involves several
hardware components, coordinated by system software. This collection of interacting
hardware and software is called the USB Battery Charging Subsystem. The following
figure shows the USBDCD module as a component of the subsystem. The following table
describes the components.
USBDCD
Module
Control
and Status
System
Software
Device
Control
Battery
Charger
IC
System Interrupt
Connector
USB Transceiver
Pullup Enable
Command
Charge
Rate
Comm
VBUS_detect
Pulldown
Enable
D
USB
Controller
USB
Bus
D
VBUS
Standard
Host Port
Dedicated
Charger
or
or
Charging
Host Port
D
D
Pullup
Enable
Module
Figure 43-8. The USB Battery Charging Subsystem
Functional Description
K20 Sub-Family Reference Manual, Rev. 6, Nov 2011
1100 Freescale Semiconductor, Inc.