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呵呵！官方提到usb hub电流不要超过2.5A。
详细改进如下：
For Applications Which Rely on the GPIO Header
There has been a small change to the GPIO pin out of revision 2.0, to add ARM JTAG support and to present a different I2C peripheral from that which is (heavily) used on the camera interface. Users wishing to produce portable GPIO code should either avoid using these pins, or add code to check the board revision and use this result to drive the correct pins appropriately.
Reset
A reset circuit has been implemented, although in the standard build the required header is not fitted. Users wishing to use this circuit should fit an appropriate header to P6. Shorting P6 pin 1 to P6 pin 2 will cause the BCM2835 to reset.
USB Output Power
The resettable fuses protecting the USB outputs have been removed. This feature was implemented on some later revision 1.0 PCBs by replacing the fuses with links; revision 2.0 permanently implements this modification. It is now possible to reliably power the RPI from a USB hub that back feeds power, but it is important that the chosen hub cannot supply more than 2.5A under fault conditions.
JTAG Debug Support
Two GPIO pins have been interchanged to allow a missing debug signal (ARM_TMS) to appear on P1 pin 13.
Original Connections Revised Connections
CAM_GPIO [BCM2835/GPIO27] routed to S5 pin 11 CAM_GPIO [BCM2835/GPIO21] routed to S5 pin 11
GPIO_GEN2 [BCM2835/GPIO21] routed to P1 pin 13 GPIO_GEN2 [BCM2835/GPIO27] routed to P1 pin 13
I2C Support on P1/P6
The primary and secondary I2C channels have been reversed.
Original Connections Revised Connections
SCL0 [BCM2835/GPIO1] routed to P1 pin 5 SCL0 [BCM2835/GPIO1] routed to S5 pin 13
SDA0 [BCM2835/GPIO0] routed to P1 pin 3 SDA0 [BCM2835/GPIO0] routed to S5 pin 14
SCL1 [BCM2835/GPIO3] routed to S5 pin 13 SCL1 [BCM2835/GPIO3] routed to P1 pin 5
SDA1 [BCM2835/GPIO2] routed to S5 pin 14 SDA1 [BCM2835/GPIO2] routed to P1 pin 3
Version Identification Links
The four GPIO signals originally used for version identification have been removed. These were never read by the system software and were redundant.
Additional I/O Expansion
To utilise GPIO signals released by the removal of the version identification links, a new connector site P5 has been added. This carries the four GPIO signals [BCM2835/GPIO28 – BCM2835/GPIO31] named GPIO7 – GPIO10 respectively, along with +5V0, +3V3 and two 0V. Currently this connector is not populated.
This GPIO allocation provides access to one of:
SDA0, SCL0 (Operating independently of P1 SDA1, SCL1); or
PCM_CLK, PCM_FS, PCM_DIN, PCM_DOUT or I2S; or
Four GPIO signals.
This connector is intended to be a suitable attachment point for third-party clock and audio codec boards, and is pinned to be mounted (ideally) on the underside due to connector clash. Pin 1 is marked with the square pad (top left - looking from the top).
+5V0 Leakage from HDMI
Some users have found that connecting an unpowered Raspberry Pi to an HDMI television interferes with the correct operation of CEC for other connected devices. This was fixed on some later revision 1.0 PCBs by removing the ESD protection diode D14; revision 2.0 fixes this issue by connecting the top side of the diode to +5V0_HDMI.
SMSC +1V8
The SMSC 1V8 power has been disconnected from the system supply.
Mounting Holes
Two 2.5mm (drilled 2.9mm for M2.5 screw) non plated mounting holes have been provided to assist with ATE (automatic test equipment) test mounting. Positions of these holes relative to the bottom left of the PCB (Power Input Corner) are:
Corner: 0.0mm,0.0mm
First Mount: 25.5mm,18.0mm
Second Mount: 80.1mm, 43.6mm
Warning: If used to permanently mount the PCB – do not over tighten screws or drill out to fit larger screws, as this will lead to irreversible PCB damage.
LED Marking
Two minor changes have been made to the silk screen:
D9 (Yellow LED) graphic changed from the incorrect 10M to 100
D5 (Green LED) graphic changed from OK to ACT (Activity)
Material Source and Accuracy
With the exception of the opening statement on increased memory capacity and board revision codes for the higher memory capacity version, the materials for this document have been sourced and published, with permission, from The Raspberry Pi Foundation. This document reflects the accuracy of the content at this stated source. The original material can be found at www.raspberrypi.org/archives/1929. |
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