12-22 Intel® PXA26x Processor Family Developer’s Manual
Universal Serial Bus Device Controller
address for the 16 x 8 data FIFO that can be used to transmit and receive data. Endpoint 0 also has
a write count register that is used to determine th e number of by tes t he U SB ho st con troll er has sent
to endpoint 0.
12.6.1 UDC Control Register
The UDC control register (UDCCR) contains seven control bits: one to enable the UDC, one to
show activity, and five to show status and associated con trol functions.

12.6.1.1 UDC Enable

The UDC Enable (UDE) bit enables the UDC. When UDE is set to a 1, the UDC is enabled for
USB serial transmission or reception. When UDE is set to a 0, the UDC is disa bled and the UDC+
and UDC- pins are three-stated. This means that the UDC ignores all activity on the USB bus.
If UDE is set to a 0 the entire UDC design is reset. If the reset occurs while the UDC is actively
transmitting or receiving data, it stops immedi atel y an d the rema inin g b its i n the tr ansm it or r eceive
serial shifter are reset. All entries in the transmit and receive FIFO are also reset.

12.6.1.2 UDC Active

The read-only UDC Active (UDA) bit can be read to determine if the UDC is currently active or in
a USB reset. This bit is only valid when the UDC is enabled. A zero indicates that the UDC is
currently receiving a USB reset from the host. A one indicates that the UDC is currently invo lved
in a transaction.

12.6.1.3 UDC Resume (RSM)

When the UDC is in a suspend state, this bit can be written to force the UDC into a non-idle state
(K state) for 3ms to perform a remote-wake-up operation. If the host PC does not start a wake-up
sequence in 3ms, the UDC returns to the suspend mode. This bit is a trigger bit for the UDC and is
automatically cleared.

12.6.1.4 Resume Interrupt Request (RESIR)

The resume interrupt request bit is set if the SRM bit in the UDC control register is cleared, the
UDC is currently in the suspended state, and the USB is driven with resume signalling.

12.6.1.5 Suspend Interrupt Request (SUSIR)

The suspend interrupt request register is set when the USB remains idle for more than 6ms. The
SUSIR bit retains state so software can determine that the USB is idle. If SRM is ze ro, SUSIR
being set will not generate an interrupt but status continues to be updated.

12.6.1.6 Suspend/Resume Interrupt Mask (SRM)

The suspend/resume interrupt mask (SRM) masks or enab les the suspend interrupt request to the
interrupt controller. When SRM is 1, the interrupt is masked and the setting of SUSIR will not
generate an interrupt. When SRM is 0, the s etting of SUS IR ge ner ates an i nterr upt when the US B is
idle for more than 6ms. Programmi ng SRM does not affect the state of SU SIR.