So, you think you need USB On-The-Go?

Agenda Introduction Embedded Host terminology OTG – Electrical – Protocol When to use OTG 2

Typical USB Network Host, Function, Hub © 2010 Renesas Electronics America Inc. All rights reserved. 3

Embedded Host Terminology Embedded Host – Not full UHCI like PC, has limited hosting capabilities defined by its Targeted Peripheral List – TPL = List of devices supported Targeted Host – Embedded Host or an OTG with a TPL Dual Role Device – MCU acts as Host and Function On different ports - at the same time On same port - at different times 4

Dual Role Device 5 HostsPeripherals Dual Role Device UHCI/OHCI Host (PC), Embedded Host Mouse, Keyboard, Flash drive, Embedded Host with FW/HW to run as Function OTG Product

USB On-The-Go Retains the Host-Function USB model, BUT – Connects Two USB devices Appears to add peer-to-peer, but negotiation who will be Host – Micro-AB receptacle with ID pin OTG has a low power advantage: – Using standard USB spec could cripple battery life of a low- powered device Regular USB Host must supply 100 mA For OTG the requirement is 8 mA Function may ask for more from Host SRP… OTG not used much due to increased complexity And since it is usually not needed! 6

Connectors and Receptacles USB Specification – Type A and Type-B plugs and receptacles – Mini A and Mini-B plugs and receptacle OTG Additions – Micro A and Micro B plugs – Micro AB receptacle Pins: – VBUS – D+ – D- – GND – ID 7 Micro A/B for OTG Micro-B plug Micro-A plug VBUS D+ D- GND ID

Host Negotiation Protocol (HNP) Method for switching Host and Function roles without disconnecting the cable Cable orientation to determine initial Host Software controlled sequence 8 USB HostUSB Function HNP

Session Request Protocol - Saves Power “Regular” USB – Suspend State mandatory after 3 ms – Function can issue Remote Wakeup – Vbus still on In OTG with SRP: – VBus turned off by Host when no activity on bus – VBus turned on after Function ‘pulses’ D+ line Need battery! Non OTG products – Hosts, including a PC or laptop, is allowed to respond to SRP. – Peripheral-Only B-device, may initiate SRP 9

Standard USB Circuitry 10

Pin Mode Host/Function/OTG Example 11 What must happen to switch between Host/Function? 1. User must pull out and reattach a cable 2. User needs to notify firmware to reinit USB (e.g. push a switch) 3. THE OUTWARD CIRCUITRY MUST CHANGE For example the YRDK62N has dipswitches that need to be altered when changing Host/function

When is OTG needed? You visit a customer that says“Our product needs both Host and Function capabilities on the same port so it needs OTG”. – True or False? – False. As we have seen, this is not the case, though action must be taken to switch between the two. 12

External Circuitry for OTG with RX62N 15 k pulldown on D+ and D- for Host mode 2.5 k pullup on D+ for Function Normal Function operation does not require the external IC OTG – IC allows VBUS to source or sink current. – MAX3355 from Maxim 13

What is required to support an OTG product? Electrical circuitry – USB Charge pumps – Supply min. 8mA /5V to Vbus USB Stack – Function stack – Host stack – OTG Specific support Host Negotiation Protocol (HNP) Session Resume Protocol (SRP) – Host/Function stack switching capability Target Peripheral List class drivers – Depending on the TPL some features above may be ignored 14

RX62N USB Peripheral Host IP based on R8A66597 – Two USB ports (Host/Function, Function only) – USB 2.0 with Full speed transfer – 10 configurable pipes (1 Control, 5 Bulk, 4 Interrupt, 2 Isochronous) – Sits on internal peripheral bus – Suspend, Resume (Host), WakeUp (Function) supported – Wakeup from deep software standby (current consumption yet to be determined) via USB activity – No Certification yet 15

Scenarios Where OTG Could be Used 1. Host - OTG acting as Function – PDA - Mouse/Keyboard/Printer – PC or Embedded Host – OTG B-device – Example: Sync a PC with a PDA/Phone/MP3/Camera 2. Host - Peripheral-Only OTG – PDA to Mouse/Keyboard/Printer – Data to/from Camera/Mp3/Phone/PDA to Flash Drive 3. OTG - OTG – Data between Camera-Phone-PDA-Mp3 16

If ‘No’ to any of these, OTG not necessary Does the product need both Host and Function capabilities? – If ‘no’ OTG not needed Is it necessary to use only one port? (One for Host and the other for Function) – No – OTG not needed Is it unacceptable to unplug and re-plug the product when switching between Host and Function roles? – No, its actually acceptable – OTG not needed Is the product expected to be used with another OTG product? – If Yes – Is that product a ‘Peripheral-Only’ No - OTG not needed Yes to ALL: – Make an OTG stack… 17

Rule of Thumb OTG is a must only if that product is expected to be used with another OTG product (which is not ‘Peripheral-Only’). If the customer still says OTG is necessary, ask the questions in the previous slide. Usually, a Dual Role Device can do the job. Wait! I need the low power solution that OTG has (SRP)! – According to the OTG standard: For non OTG products, a host, including a PC or laptop, is allowed to respond to SRP. A peripheral-Only B-device, may initiate SRP. 18

Summary Introduction The Embedded Host OTG – Electrical Spec – Protocol Spec When to use OTG? OTG in a product with Host and Device support, is a must only if that product is expected to be used with another OTG Device. In all other cases an Embedded Host can do the job. 19