1 Introduction

The TUSB21XX family of devices are USB high-speed signal conditioners intended to compensate for ISI signal losses in a transmission channel. The devices are designed to condition high-speed signals, while leaving low and full-speed signals unconditioned. For this reason, it is important to ensure that the device is enabled in high-speed mode while performing compliance testing. Some cases can arise in which the device does not detect and enable high-speed mode if test procedures are not followed exactly. The TUSB21XX devices include both a high-speed enable (ENA_HS) and connection-detected (CD) status pin to assist in ensuring proper device state prior to testing. This document details the behavior of these status pins across the testing procedure for each test mode. The expected state of each pin during testing is included in Table 1-1.

1. "High" indicates logic level 1. Voltage value varies based on supply voltage and current. For more information, see the Electrical Characteristics section of the device-specific data sheet.
2. "Low" indicates logic level 0. Voltage value will be approximately 0V. For exact values, see the Electrical Characteristics section of the device-specific data sheet.

In performing HS signal quality testing, there are three main "modes" or configurations of testing: host mode, device mode, and embedded host mode. Each of these configurations involve a slightly different test procedure and system setup. In host mode, a system sends test packets downstream, where they are received and measured. In device mode, a host system sends a test packet command to a connected device downstream. Upon receiving this command, the device sends test packets upstream, where they can be measured and analyzed. Lastly, in embedded host mode, the use of a device with a specific Vendor ID (VID) and Product ID (PID) is needed. The VID and PID are 16-bit numbers used to identify USB devices. A device with a specific combination is needed to place a controller, or embedded host, in test mode and tell it to continuously send test packets. Embedded host testing supports compliance testing for system design in which the host cannot support the USB-IF High-Speed Electrical Test Tool (HSET), such as an embedded microcontroller. The test mode compatibility across the TUSB21XX devices are detailed in Table 1-2.