National CP3BT26 - Manual (Page 90)

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CP3BT26
18.0 USB Controller
The CR16 USB node is an integrated USB node controller
that features enhanced DMA support with many automatic
data handling features. It is compatible with USB specifica-
tion versions 1.0 and 1.1.
It integrates the required USB transceiver, a Serial Interface
Engine (SIE), and USB endpoint (EP) FIFOs. Seven end-
point pipes are supported: one for the mandatory control
endpoint and six to support interrupt, bulk, and isochronous
endpoints. Each endpoint pipe has a dedicated FIFO, 8
bytes for the control endpoint and 64 bytes for the other end-
points.
18.1 FUNCTIONAL STATES
18.1.1 Line Condition Detection
At any given time, the CR16 USB node is in one of the fol-
lowing states
The NodeSuspend, NodeResume, or NodeReset line con-
dition causes a transition from one operating state to anoth-
er. These conditions are detected by specialized hardware
and reported in the Alternate Event (ALTEV) register. If in-
terrupts are enabled, an interrupt is generated on the occur-
rence of any of the specified conditions.
In addition to the dedicated input to the ICU for generating
interrupts on these USB state changes, a wake-up signal is
sent to the MIWU (see Section 13.0) when any activity is de-
tected on the USB, if the bus was in the Idle state and the
USB node is in the NodeSuspend state. The MIWU can be
programmed to generate an edge-triggered interrupt when
this occurs.
NodeOperational
This is the normal operating state of the node. In this state,
the node is configured for operation on the USB.
NodeSuspend
A USB node is expected to enter NodeSuspend state when
3 ms have elapsed without any detectable bus activity. The
CR16 USB node looks for this event and signals it by setting
the SD3 bit in the ALTEV register, which causes an inter-
rupt, to be generated (if enabled). Software should respond
by putting the CR16 USB node in the NodeSuspend state.
The CR16 USB node can resume normal operation under
software control in response to a local event in the device. It
can wake up the USB bus via a NodeResume, or when de-
tecting a resume command on the USB bus, which signals
an interrupt to the CPU.
NodeResume
If the host has enabled remote wake-ups from the node, the
CR16 USB node can initiate a remote wake-up.
Once software detects the event, which wakes up the bus,
it releases the CR16 USB node from NodeSuspend state by
initiating a NodeResume on the USB using the NFSR reg-
ister. The node software must ensure at least 5 ms of Idle
on the USB. While in NodeResume state, a constant “K” is
signalled on the USB. This should last for at least 1 ms and
no more than 5 ms, after which the USB host should contin-
ue sending the NodeResume signal for at least an addition-
al 20 ms, and then completes the NodeResume operation
by issuing the End Of Packet (EOP) sequence.
To successfully detect the EOP, software must enter the
USB NodeOperational state by setting the NFSR register.
If no EOP is received from the host within 100 ms, software
must re-initiate NodeResume.
NodeReset
When detecting a NodeResume or NodeReset signal while
in NodeSuspend state, the CR16 USB node can signal this
to the CPU by generating an interrupt.
USB specifications require that a device must be ready to
respond to USB tokens within 10 ms after wake-up or reset.
Table 38 State Descriptions
State Descriptions
NodeOperational Normal operation
NodeSuspend Device operation suspend due to
USB inactivity
NodeResume Device wake-up from suspended
state
NodeReset Device reset