TH6503 datasheet(2/24 Pages) ETC

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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

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.

TH6503

USB

Interface

to USB

Hub/Host

Endpoint 0

Endpoint 1

Endpoint 2

Interrupt

Transfer

Control

Transfer

serial

Data

Micro-

controller

Vendor specific

Data

Input

Device

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