isp1761 NXP Semiconductors, isp1761 Datasheet - Page 85

• Manufacturer Part Number: isp1761
• Description: Hi-speed Universal Serial Bus On-the-go Controller
• Manufacturer: NXP Semiconductors

NXP Semiconductors
9. OTG Controller
ISP1761_4
Product data sheet
9.1 Introduction
9.2 Dual-role device
OTG is a supplement to the Hi-Speed USB specification that augments existing USB
peripherals by adding to these peripherals limited host capability to support other targeted
USB peripherals. It is primarily targeted at portable devices because it addresses
concerns related to such devices, such as a small connector and low power. Non-portable
devices, even standard hosts, can also benefit from OTG features.
The ISP1761 OTG Controller is designed to perform all the tasks specified in the OTG
supplement. It supports Host Negotiation Protocol (HNP) and Session Request Protocol
(SRP) for dual-role devices. The ISP1761 uses software implementation of HNP and SRP
for maximum flexibility. A set of OTG registers provides the control and status monitoring
capabilities to support software HNP and SRP.
Besides the normal USB transceiver, timers and analog components required by OTG are
also integrated on-chip. The analog components include:
When port 1 of the ISP1761 is configured in OTG mode, it can be used as an OTG
dual-role device. A dual-role device is a USB device that can function either as a host or
as a peripheral.
The default role of the ISP1761 is controlled by the ID pin, which in turn is controlled by
the type of plug connected to the mini-AB receptacle. If ID = LOW (mini-A plug
connected), it becomes an A-device, which is a host by default. If ID = HIGH (mini-B plug
connected), it becomes a B-device, which is a peripheral by default.
Both the A-device and the B-device work on a session base. A session is defined as the
period of time in which devices exchange data. A session starts when V
ends when V
During a session, the role of the host can be transferred back and forth between the
A-device and the B-device any number of times by using HNP.
If the A-device wants to start a session, it turns on V
B-device detects that V
of a peripheral asserting its pull-up resistor on the DP line. The A-device detects the
remote pull-up resistor and assumes the role of a host. Then, the A-device can
communicate with the B-device as long as it wishes. When the A-device finishes
communicating with the B-device, the A-device turns-off V
go into the idle state. See
If the B-device wants to start a session, it must initiate SRP by ‘data line pulsing’ and
‘V
(Note: only the A-device is allowed to drive V
•
•
•
•
BUS
Built-in 3.3 V-to-5 V charge pump
Voltage comparators
Pull-up or pull-down resistors on data lines
Charging or discharging resistors for V
pulsing’. When the A-device detects any of these SRP events, it turns on its V
BUS
is turned off. Both the A-device and the B-device may start a session.
BUS
Rev. 04 — 5 March 2007
Figure 15
has risen above the B_SESS_VLD level and assumes the role
and
Figure
BUS
BUS
16.
.) The B-device assumes the role of a
BUS
by enabling the charge pump. The
BUS
Hi-Speed USB OTG controller
and both the devices finally
© NXP B.V. 2007. All rights reserved.
BUS
ISP1761
is driven and
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BUS
.