Digi NS9750 - Manual (Page 732)

O v e r v i e w
7 0 8 N S 9 7 5 0 H a r d w a r e R e f e r e n c e
Overview
USB consists of point-to-point connections between one host and any number of hubs
and devices; the number of hubs and devices combined cannot exceed 127. Point-to-
point connections are established between a downstream port and an upstream port,
as shown:
USB module architecture
The USB module is comprised of a separate host block and device block (see Figure
101). You can enable the device block or the host block — but never both at the same
time.
The device block provides the resources for 12 logical endpoints that can be
reconfigured by the device driver. The device block includes a DMA function to
preload data for in endpoints, stuff data for out endpoints into system memory, and
stuff data for some packets into system memory.
Host/hub/device Description
Host Has one downstream port
If has multiple downstream ports, constitutes multiple networks
Hub Has one upstream port and multiple downstream ports
Connects to devices or other hubs using downstream ports
Connects to hosts or other hubs using upstream ports
Device Has one upstream port
Connects to hubs or hosts