Retinal Prosthesis Dissertation - Student Home Pages

5.5.1 Incoming (short) AER stream
The `short’ AER stream for a 16 pixel image consists of 8 address bits and 18 bits of
colour plane information. This initial component (preform_for_electrodes) simply
produces 8 address bits and 6 bits of colour information - this encoding of the integer
range 0..63 holds the pulse count of up to 50 pulses for maximum intensity; for each
plane of colour.
5.5.2 Production of colour data streams
The pulse count for each plane is now converted (produce_colour_data_streams) to a
50 bit representation whereby each bit of value one is an active pulse and of value
zero inactive i.e. no pulse. At this stage of the processing, within the FPGA fabric,
the value of one means that the next stage of the processing will recognise that an
innerpulse aka biphasic pulse representing a spike aka, an action potential in
biological terminology, occurs within an outerpulse.
5.5.3 Convert to long format
For the red, green and blue planes the colour data stream held in fifty bits is now
converted so that each outerpulse is represented by twenty bits where four bits
represent the `spike’ aka as the innerpulse and the remaining 16 bits represent the off
time of the outerpulse. Therefore the information for a full pixel for each plane is
held in 1000 bits.
5.5.4 Production of output streams
Using a case statement enables 250 blocks of four bits to be sent to each of the
outgoing wires (sixteen for each colour) equally spaced over a second where those
100 of 200