UPSD3422_06 Datasheet, PDF (144/293 Pages) STMicroelectronics – Turbo Plus Series Fast Turbo 8032 MCU with USB and Programmable Logic

USB interface
uPSD34xx
Figure 49. USB module block diagram
Clock
D–
USB–
D+
USB+
USB
Transceiver
3 - 40MHz
PLL
Endpoint4
48MHz
Endpoint0
IN FIFOs (64 bytes each)
Serial
Interface
Engine
FIFO Interface Logic
OUT FIFOs (64 bytes each)
Endpoint0
8032
MCU
S
F
XDATA
R
CTRL
B
u
s
USB SFRs
CTRL and Data
Endpoint4
CTRL
SETUP Command
Buffer (8 bytes)
CTRL and Data
AI10488
25.1
25.1.1
Basic USB concepts
The Universal Serial Bus (USB) is more complex than the standard serial port and requires
familiarity with the specification to fully understand how to use the USB peripheral in the
uPSD34xx. The USB specification is available on the Internet at http://www.usb.org. Some
basic concepts will be presented in this section but knowledge of the USB specification is
required.
In a USB system, there is only one master and the master is the host computer. The host
controls all activity on the bus and devices respond to requests from the host. The only
exception is when a device has been put into a low power suspend mode by the host. In this
case, the device can signal a remote wakeup. Outside of that exception, all activity is
controlled and initiated by the host. The host-centric model versus a peer-to-peer model
provides the best way to develop low cost peripherals by keeping the complex control logic
on the host side. The uPSD34xx is a peripheral (non-host) device.
Communication flow
The USB provides a means for communication between host (client) software and a function
on a USB device. Functions can have different requirements for the communication flow
depending on the client software to the USB function interaction. With USB, the various
communication flows are separated to provide better bus utilization. For example, one
communication flow is used for managing the device while another is for transferring data
related to the operation of the device. Some bus access is used for each communication
flow with each flow terminated at an endpoint on a device. Each endpoint has various
aspects associated with the communication flow. A USB device looks like a collection of
endpoints to the USB system.
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