Cypress EZ-USB Series 2100 User's Guide download pdf (Page 213)

Bulk Transfers with the EZ-USB

SX2™ connected to an Hitachi SH3™ DMA Interface

Writing Commands to the SX2

There are two types of Command Write sequences in a typical application: downloading vendor and application specific descriptor

contents and setting indexed SX2 control register contents.

1. The first Command Write sequence is for downloading custom descriptor information into the SX2, which the SX2 will then

use during subsequent USB enumerations. There are two types of descriptor downloads. The first method is for downloading

only Vendor ID (VID), Product ID (PID) and Device ID (DID) information. This sequence consists of loading a six byte only

sequence consisting of VID, PID, and DID. The SX2 will enumerate with its default interface and endpoint configurations. The

second method is for downloading complete descriptor information including interface and endpoint configuration information.

In this case, the SH3 writes a Command Byte, with the Descriptor Register index, followed by the descriptor length, and then

downloads the descriptor contents. The descriptor can be up to 500 bytes in length and includes both high-speed and full-speed

descriptors (see the SX2 data sheet sections 4.1 and 4.2 for downloading descriptors and section 12 for the default descriptors).

2. The second Command Write sequence is for programming the SX2 control registers. This sequence consists of writing a

Command Byte followed by two data bytes. The Command Byte consists of a direction bit (for write or read register contents)

and a register index. The first data byte consists of the most significant 4 bits of the control setting and the second data byte

consists of the least significant 4 bits of the control setting.

Figure 2. SX2 Command Write Signals

1 2 ... 208 209 210 211 212 213 214 215 216 217 218 ... 238 239

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Cypress EZ-USB Series 2100 User's Guide Page 213