41
Sensor reference voltages are presented to the DAC's exactly as they are stored in the
state. The order listed above is the recommended order, but other orders may work. The
format for these is MS byte first with the most significant nibble indicating the command
code to the DAC. Pairs of values are sent, one to each DAC chip with the first going to
U25 and the second to U26. Voltages are updated in the order sent. Default values
shown are for the FastCamera 13. For more information see the LTC1660 data sheet.
Whenever the state memory is updated from host or flash, the actual internal registers that
implement the camera state also change. Some of these are located in the Control FPGA
and some in the Data FPGA. The Control FPGA forwards state data to the Data FPGA
whenever it is updated.
The state memory holds all of the state variables currently defined for camera operational
modes as well as some additional storage that can be defined as required for more
sophisticated Data FPGAs. The Data FPGAs can count on this storage to be refreshed
from flash after initial FPGA load and whenever the user restores state from one of the
saved sets in flash.
In addition to the camera state storage pages, some of the flash memory is available for
Data FPGA storage requirements such as pixel defect maps. The amount of flash
available for this depends on the size of the Data FPGA and the size of the flash device. A
pointer in the flash header in page zero indicates the starting page of the Data FPGA
initialization area. Its length in pages (which may be zero) is stored in the flash header as
well. Data from this initialization area is read out and sent to the data FPGA after initial
FPGA load. Although the data in these pages has no predefined layout, the first page
must start with the sequence 3C, A5, 0F, 96. This prevents transmission of uninitialized
flash pages and serves to identify the following data as Data FPGA Initialization Data
rather than Camera State.
Serial Camera Control Interface
S
ERIAL
C
ONTROL
I
NTERFACE
Encoding
Commands and response use the 7-bit ASCII code zero-extended to 8 bits. This is
sometimes referred to as 8 bits, no parity or 7-bits space parity. For characters that
require escape codes as listed below, the 8th bit is significant in the decoding, so only the
normal character encoding needs to be escaped. For example hex 0d requires the escape
sequence but hex 8d does not.
