Overview
13-8
13.1.6 Software Disconnect
The PULLUP_EN (0) bit of the SYSCON1 register allows the device to discon-
nect itself from the USB.
This bit is by default directly connected to the OMAP5910 pad (USB.PUEN),
which must be connected on the application board to a 1.5-k
Ω
resistor.
The other pin of the resistor must be connected to the positive differential line
(OMAP5910 pad USB.DP) of the USB (D+).
Thus:
-
PullUp_En bit=0 (by default): The external 1.5-k
Ω
is seen as a pulldown
on the USB D+; the external USB host cannot detect the OMAP5910 USB
function.
-
PullUp_En bit=1: The external 1.5-k
Ω
is seen as a pullup on the USB D+,
the USB host detects this level and, therefore, the presence of the
OMAP5910 USB function. The USB host can then configure the USB
function.
The USB.PUEN signal is multiplexed inside OMAP5910 with the USB.CLKO
clock. Bits (5:3) of the FUNC_MUX_CTRL_D register control this multiplexing:
-
FUNC_MUX_CTRL_D(5:3)= 000 (default): USB.PUEN signal is output.
-
FUNC_MUX_CTRL_D(5:3)= 001: USB.CLKO clock is output.
The USB.CLKO clock comes from the ULPD DPLL after an internal dividing
by 8 (6 MHz) (see Chapter 15, Clock Generation and System Reset Manage-
ment for more details). This clock is dedicated to an external USB HUB.