Difference between revisions of "USB"
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Revision as of 09:23, 19 June 2009
| USBH_PWR1 | Over-current fault indicator (input, active low) | |
| USBH_PEN1 | Power enable USB port (output) | |
| USBH_P1 | USB port | USB D+ |
| USBH_N1 | USB D- | |
| V_BATT | USB VBUS | |
| GND | USB DGND | |
The 24-pin flex ribbon connector has USB Host port 1 on it. USB Host port 2 is on the 60-pin Hirose connector
The pinouts you need for USB Host port 1 are:
- V_BATT (pin 24) - USB power
- USBH_N1 (pin 18) - USB D-
- USBH_P1 (pin 17) - USB D+
- GND (pin 8) - USB Ground
In addition, you need to pull USBH_PWR1 (pin 20) up to 3.3 volts to enable the port (this is a hack, USBH_PEN1 and USBH_PWR1 should be routed to a power switch IC -for example TPS2041B- to power the USB port and monitor over-current/short-circuit conditions). You need to provide a stable 3.3 volt supply, which is fairly simple to do by adding a small SOT23 package voltage regulator (like the LM3480), with the power input coming from V_BATT (pin 24) and the output going to USBH_PWR1 (pin 20).
USBH_N1 and USBH_P1 (D-/D+) require 15K pull-down resistors each, 10-25 ohm series resistors and 68-75pF capacitors. ESD protection/transient suppression is recommended (example: SN65220 single port transient suppressor).
Refer to the PXA270 Design Guide, P. 202 (link on the bottom of this page) for more information.
Examples
File:24pin-connector-usb-example.png
USB Host example without ESD and over-current protections (not fully USB-compliant)
Related
Universal Serial Bus Revision 2.0 specification
Open HCI—Open Host controller Specification for USB
Implementing the Physical Layer in a USB 2.0 Compliant System, AN-5052, Fairchild Semiconductor
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