Interfacing a camera module (Was: Weird hardware mod ???)

[Rask Ingemann Lambertsen]

On Sun, Apr 19, 2009 at 03:50:02PM +0200, Rask Ingemann Lambertsen wrote:

>    We do however have a completely unused SPI interface going to the debug
> board connector and nearby test points H-TP4715 - H-TP4718. The SC32442B
> manual doesn't say how fast the SPI interface can go as a slave device, but
> even if the 25 MHz maximum specified for master mode is also the maximum for
> slave mode, it would be a substantial improvement over USB 1.1. This could
> be useful because:
>  a) There are cameras which output image data over a serial bus[2].
>  b) There are chips to convert a camera parallel bus to a serial bus[1].
> Both use differential signalling on the serial output, though. Also, the
> device [1] is not bit transparent, for example, so 10-bit Bayer and JPEG
> formats are not supported. A plain old shift register and a x8 PLL oscilator
> for the serial clock would do the trick.

   The shift register could be a standard 74166 if you find one that runs
quickly enough[1], but it would be better to find one which includes the
logic to signal that the last bit has been shifted out (need for extending
the line sync at the end of each line). The x8 PLL is trickier. Finding one
that accepts low enough input clocks is difficult, but not impossible[2].

[1] http://www.ti.com/lit/gpn/sn74lv166a
[2] http://www.idt.com/index.cfm?genID=570

>    The cameras tend to use 1.8 V, 2.5 V or 2.8 V, so some level shifting on
> at least the I2C bus (debug connector or test points H-TP4703 and H-TP4704)
> is necessary.

   I2C bus level shifting solved[1]. For a serial output camera, the
differential line receiver will do the trick.

[1] http://www.ti.com/lit/gpn/pca9306

-- 
Rask Ingemann Lambertsen
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