SLYT834 March   2023 ISOUSB211

 

  1. 1 Introduction
  2. 2 Existing implementation of OTG USB applications
  3. 3  On-the-go operation
  4. 4 Implementation of isolated OTG
  5. 5 Demonstration of OTG with ISOUSB211 EVM
  6. 6 Scenario A: Isolated OTG module connected to a USB-drive (bus-powered)
  7. 7  Scenario B: Isolated OTG module connected to a laptop (host)
  8. 8 Demonstration
  9. 9 Connect phone to laptop
  10. 10Connect phone to USB-drive
  11. 11Summary

3 On-the-go operation

OTG ports have an additional fifth pin tagged as the ID pin. The status on this ID pin governs the initial host and peripheral roles when the connect occurs, as shown in #FIG_JVZ_RK1_MVB. The port connected to the cable end with ID shorted to ground assumes the initial host (A-device) role and the device connected to the other end of cable with ID left floating assumes the initial peripheral role (B-device). The ID pull-up on the OTG module helps determine the status of ID pin on connect. In a situation where the B device wants to take over the host role, OTG defines an HNP that enables devices to exchange roles seamlessly without unplugging and exchanging the cable connections. For HNP to work seamlessly, the isolated USB repeater should have the ability to switch any side to be upstream- or downstream-facing on the fly. The Session Request Protocol that enables the initiation of sessions on the A device by pulsing on the VBUS is not a topic that is covered in this article.

Figure 3-1 Initial Host or peripheral roles determined by ID pin.