Filter
Top Products
262 SA-1110 Developer’s Manual
Peripheral Control Module
Hosts and hubs have pull-down resistors on both the D+ and D- lines. When a device is not attached
to the cable, the pull-down resistors cause D+ and D- to be pulled down below the single-ended low
threshold (0.8 volts) of the Host or hub. This creates a state called single-ended zero (SE0). A
Disconnect is detected by the Host when a SE0 persists for more than 2.5 µs (30-bit times). When the
SA-1110 UDC is connected to the USB cable, the pull-up resistor on the UDC+ pin causes D+ to be
pulled above the single-ended high threshold level. After 2.5 µs elapses, the Host detects a connect.
At this point, the bus is in the Idle state because UDC+ is high and UDC- is low. A Start Of Packet
is signaled by transitioning the bus from the Idle to the Resume state (a 1 to 0 transition). The
beginning of each USB packet begins with a Sync field, which starts with the 1-to-0 transition (see
the Section 11.8.1.1, “Signalling Levels” on page 11-261). After the packet data has been
transferred, an End Of Packet is signaled by pulling both UDC+ and UDC- low for 2-bit times,
followed by an Idle for 1-bit time. If the Idle persists for more than 3 milliseconds, the SA-1110
UDC enters Suspend mode and it is placed in low-power mode. The SA-1110 UDC can be
awakened from Suspend mode by the Host switching the bus to the Resume state via normal bus
activity, or by signaling a Reset. Under normal operating conditions, the Host periodically signals a
Start of Frame (SOF) to the SA-1110 UDC to ensure that the SA-1110 UDC does not enter the
Suspend mode.
11.8.1.2 Connecting the USB to the SA-1110
Figure 11-14 shows how the USB should be connected to the SA-1110.
Disconnect UDC+ AND UDC- below single-ended low threshold (0.8 volts) for more than 2.5 µs.
(Disconnect is the static bus condition that results when no device is plugged into a hub
or Host port.) Note: Disconnect is not sensed by the SA-1110 UDC; rather, GPIOn in
Figure 11-14 is used to indicate disconnection of the USB cable.
Connect
UDC+ OR UDC- high for more than 2.5 µs.
Reset
UDC+ AND UDC- low for more than 2.5 µs. (Reset is driven by the Host and sensed by
the SA-1110 UDC.)
Table 11-11. USB Bus States
Bus State UDC+/UDC- Pin Levels