Great work.MattHawkinsUK wrote:I received my Rev 2 board and the first thing I did (after powering it up) was testing the P5 pins to work out how the GPIO connections were arranged.
Here is the results :
Raspberry Pi P5 Header
http://www.raspberrypi-spy.co.uk/2012/0 ... p5-header/
No, each generic I/O pin can fulfill several functions, which one function it fulfills is determined by software.wallarug wrote:Just saw that. Great Work! What are the ALT functions though? Is that one for the foundation to release?MattHawkinsUK wrote:Done.
Yes:DogEars wrote:Is there such a thing as an 8-way ribbon type connector, I've tried looking, but can only find a Molex connector that has to have each pin individually crimped and inserted into a plastic housing.
I am aware of all of the above. But, some of the pins on P1 seem to have very specific ALT functions. From what your seem to be saying above, I can program the pins (through s/ware) to do whatever I want. I don't know if I am correct in saying that. Can you confirm this? I am new to hardware hacking and the such.mahjongg wrote:No, each generic I/O pin can fulfill several functions, which one function it fulfills is determined by software.wallarug wrote:Just saw that. Great Work! What are the ALT functions though? Is that one for the foundation to release?MattHawkinsUK wrote:Done.
All generic I/O pins (note that not calling it a GPIO pin is intentional, to avoid confusion) default to a simple basic input/output pin, a pin that can be directly controlled, as an input pin, one that can be read out, to deliver a single binary value, or can be programmed as output that can be programmed high or low.
Depending on the exact pin number the pin can also be controlled by one or more specific I/O mechanisms, called an "alternative function". Such a mechanism can for example be a "UART", a "Universal Asynchronous Receiver/Transmitter". an electronic device that converts a parallel signal into an (asynchronous) serial bitstream, (Transmitter) and can convert such a bitstream back into a parallel signal. Its the basis for what you might know as the RS232 port.
Other mechanisms for example assists in interfacing to external devices such as those using the I2C (inter-IC-communication) interface, or the SPI (Serial Peripheral Interface bus) signal, or the I2S (inter-IC sound interface). A "PWM", (pulse width modulation) mechanism automatically outputs a pulse stream where the ratio between the signal being high and the signal being low can be controlled in software, but the software doesn't have to create a pulse stream itself (by toggling the output high and low in succession). This one can be used to control a servo, create a variable analog output level (by simply filtering the signal with a resistor and capacitor), or control a servomotor.
not every pin has the same mechanisms "behind it", but often you can choose from several alternatives (ALT functions) to the standard general purpose I/O function.
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).
Code: Select all
GPIO# ALT0 ALT1 ALT2 ALT3 ALT5 28 SDA0 SA5 PCM_CLK <reserved> 29 SLC0 SA4 PCM_FS <reserved> 30 <reserved> SA3 PCM_DIN CTS0 CTS1 31 <reserved> SA2 PCM_DOUT RTS0 RTS1
On the top there is not enough room with the 26 way socket in place, if mounted underneath it makes the board deeper and if it is mounted on a board or in a box then you have to remove the board to add the socket.wallarug wrote:Why can't you just use a vertical header? ie. all the headers would be in the same direction next to each other.
Did you test this situation? I don't have a Model B rev2 so I am just guessing, If you have tested then you are probably right.Grumpy Mike wrote:On the top there is not enough room with the 26 way socket in place, if mounted underneath it makes the board deeper and if it is mounted on a board or in a box then you have to remove the board to add the socket.wallarug wrote:Why can't you just use a vertical header? ie. all the headers would be in the same direction next to each other.
I am only reporting what I found and what I did. However what ever works for you is good.
Did you test this situation?
ok.Grumpy Mike wrote:Did you test this situation?
Well I didn't solder the header into the top of the board but when I put it in the holes and offered up the connectors they looked too tight to me. That is why I went with the solution I did.
Can some explain SDA and SCL channels to me...I am confused.Pin 3 (SDA0) and Pin 5 (SCL0) are preset to be used as an I²C interface. So there are 1.8 kilohm pulls up resistors on the board for these pins.
Pin 12 supports PWM.
These are the two signals Serial DAta and Serial CLock that are used in the I2C interface. Nothing to do with the PWM.Can some explain SDA and SCL channels to me