TH6503 Datasheet, PDF (2/24 Pages) List of Unclassifed Manufacturers – USB Low-Speed Interface

TH6503 USB Low-Speed Interface
Function
USB Data Transmission
The TH6503 supports the USB Specification 1.1
data model.
Data from the USB host to the device and vice
versa is transmitted serially. The data are NRZI
coded to increase transmission reliability; bit
stuffing (inserting an extra 0 bit after any
6 consecutive 1 bits) is performed and a CRC check
carried out. Bit stuffing, NRZI coding/decoding and
CRC checks or generation are performed within the
TH6503.
The data is transmitted in packets. Three types of
packets are defined for the USB: token, data and
handshake.
The token is always passed on by the host.
It contains a PID (packet identifier) which defines the
direction of the following data transmission and the
address of the device and endpoints to be ad-
dressed.
Depending on the previous token command, data is
transferred from the USB host to the TH6503 (OUT
transfer) or transferred from the TH6503 to the USB
host (IN transfer). In the process the respective
FIFOs are written (OUT) or read (IN).
The data transfer is concluded with a handshake.
If the data has been received successfully, an ACK
is sent to the data source. If no data is ready for an
IN transfer out of the TH6503, it sends an NAK
handshake instead of the data (if endpoint is ena-
bled).
TH6503/
Microcontroller
Cooperation
to USB
Hub/Host
TH6503
USB
Interface
Interrupt
Transfer
Control
Transfer
Endpoint 2
Endpoint 1
Endpoint 0
serial
Data
Micro-
controller
Vendor specific
Data
Input
Device
Figure 2. Data Flow
The TH6503 is responsible for the data flow be-
tween the USB and the microcontroller. It ensures
that the USB transfers the data in line with the
protocol. All information in the protocol layer is
decoded by the TH6503 and carried out accord-
ingly.
The data arriving from the USB host is stored in a
FIFO buffer until it is collected by the microcontroller.
Data transmitted to the USB host are imported
from a FIFO buffer which has previously been filled
by the microcontroller. A /INT signal signals to the
microcontroller that the FIFO status has been
changed by USB.
Data is transferred between the microcontroller
and the TH6503 via a software-emulating serial
interface controlled by the microcontroller.
As the TH6503 cannot interpret the content of the
data, it must be evaluated within the microcontroller.
This also applies to USB-specific control informa-
tion. All USB-typical descriptors and the associ-
ated requests must be created and managed by
the microcontroller.
The setting of the USB address serves here as an
example. After resetting the USB, the address is
set to the default value 0 (USBAddressRegister). A
specific address is transferred from the USB host
software to the device with the SET_ADDRESS
command. This command, like all SET and GET
commands, can only be decoded by the micro-
controller. The USB address is decoded in the
TH6503 with the aid of the USB AddressRegister.
For this reason the microcontroller must write the
USB address determined in this register.
The TH6503 supports the USB suspend mode.
Control takes place via the microcontroller. The
ACT bit can be used in the StatusRegister <5>
which is set on the USB for each activity. If this bit
has been inactive for a longer period of time (3 ms),
the microcontroller can set the TH6503 and itself in
the suspend mode using the SUS bit in the
BridgeConfigRegister <4>. The suspend mode
can be ended using the software or an external
signal. Apart from the suspend mode, the TH6503
also supports a number of other power saving
modes which either stop the microcontroller by
switching off the clock or set the whole USB bridge
in a power saving mode.
The TH6503 provides the clock pulse for the
microcontroller. It can be programmed with the
OCR 1 - OCR 0 bits in the BridgeConfigRegister
<1-0>.
The TH6503 supplies 3.3V voltage to power the
microcontroller; this is produced by the adjacent
5V bus power supply connection.
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