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Doc ID 7215 Rev 4
11.3 USB INTERFACE (USB)
11.3.1 Introduction
The USB Interface implements a full-speed func-
tion interface between the USB and the ST7 mi-
crocontroller. It is a highly integrated circuit which
includes the transceiver, 3.3 voltage regulator, SIE
and USB Data Buffer interface. No external com-
ponents are needed apart from the external pull-
up on USBDP for full speed recognition by the
USB host.
11.3.2 Main Features
■ USB Specification Version 2.0 Compliant
■ Supports Full-Speed USB Protocol
■ Five Endpoints (including default endpoint)
■ CRC
generation/checking,
NRZI
encoding/
decoding and bit-stuffing
■ USB Suspend/Resume operations
■ Special Data transfer mode with USB Data
Buffer Memory (2 x 512 bytes for upload or
download) to DTC
■ On-Chip 3.3V Regulator
■ On-Chip USB Transceiver
11.3.3 Functional Description
of the USB interface hardware.
For general information on the USB, refer to the
“Universal Serial Bus Specifications” document
available at http//:www.usb.org.
Serial Interface Engine
The SIE (Serial Interface Engine) interfaces with
the USB, via the transceiver.
The SIE processes tokens, handles data transmis-
sion/reception, and handshaking as required by
the USB standard. It also performs frame format-
ting, including CRC generation and checking.
Endpoints
The Endpoint registers indicate if the microcon-
troller is ready to transmit/receive, and how many
bytes need to be transmitted.
Data Transfer to/from USB Data Buffer Memory
When a token for a valid Endpoint is recognized by
the USB interface, the related data transfer takes
place to/from the USB data buffer. In normal con-
figuration (MOD[1:0] bits=00 in the CTLR register),
at the end of the transaction, an interrupt is gener-
ated.
Interrupts
By reading the Interrupt Status register, applica-
tion software can know which USB event has oc-
curred.
Figure 36. USB Block Diagram
CPU
Transceiver
3.3V
Voltage
Regulator
SIE
ENDPOINT
BUFFER
USB
Address,
and interrupts
USBDM
USBDP
USBVCC
48 MHz
REGISTERS
data busses
USBGND
BUFFER
USB
DATA
INTERFACE
1