Black Spot Hardware
Regulators and passive components
Blackfin BF533 DSP
Figure 5.6 A block diagram of the main camera module components.
schematic was designed that allows the Blackfin to be interfaced to the image sensor
and data from the Blackfin to be sent to the hub. This involved choosing parts to supply the Blackfin and image sensor with the power supplies, clocks, and data buses that they require. It also requires a method to allow the boards to be programmed, debugged, and connected to the hub. The board design was based around the open source BlackfinONE project . block diagram of the board’s main components is shown in Figure 5.6. This diagram shows the Blackfin connected to a serial flash chip, image sensor, headers, and surrounded by supervisor and passive components. The flash chip stores the program code that the Blackfin executes. This is loaded into the Blackfin by an on-chip bootloader
during start-up. On the left of the figure is the JT
G debugging header. This allows code to
be loaded into the Blackfin’s internal SR
M by a PC bypassing the flash during debugging
of the firmware. Below the JT G header the is interfaced to each camera module through
communications header is shown. The hub the communications header. This connector
also carries power and timing signals. The interfacing discussed in more detail in the following sections.
Image sensor interface
The image sensor is connected to the Blackfin via a parallel interface and also via a two- wire interface (TWI). The parallel interface is used to transfer the image data from the sensor to the processor. This comprises a 10 bit data bus and five timing signals. Only the 8 most significant bits are connected to the Blackfin to reduce the memory required. The DM controller in the Blackfin is capable of transferring 16 bit data and, therefore, could transfer 10 bit image data. However, this would require twice as much memory as 8 bit data because each 10 bit word would be stored using 16 bits within the Blackfin’s memory. The TWI is used to transfer sensor initialisation, control, and status information. This bus is used by the processor to set the image sensor resolution, shutter period, and other sensor