asciicod.m

通信系统的matlab仿真程序

function [sys,x0] = asciicod(t,x,u,flag,period,width,source)
%ASCIICOD generate pulse signal based on ascii coding 
%     There will have not pulse generated until a non-zero
%   input pulse is received. 

%       Wes Wang
%       Copyright (c) 1995-96 by The MathWorks, Inc.
if flag == 2     %refresh states
       sys = x;
        if (u ~= 0) & (x(1) == 0)
               sys(1) = 1;
             sys(5) = width;
 end;
    if x(1) == 1
            %update the discrete-time states

                %x(2) increases at 4*8 rate
             sys(2) = rem(x(2)+1,16);

                %x(3) indicates the next character
              if sys(2) == 1
                  sys(3) = sys(3) + 1;
                    %when transfer is done.
                 if sys(3) > sys(4)
                              sys(1) = 2;
                     end;
            end;

            %update the next time increament x(5)
           phase_in_pulse = sys(2) - floor(sys(2) / 2) * 2;
                if phase_in_pulse == 1
                  sys(5) = width;
         else
                    sys(5) = period / 8 - width;
            end;

            %update the next output pulse.
          sys(6) = 0;
             if ((phase_in_pulse == 1) & (sys(3) <= sys(4)))
                 cur_char = sprintf('%o', source(sys(3)));
                       len_cur_char = length(cur_char);
                        while len_cur_char < 3
                          cur_char = ['0', cur_char];
                             len_cur_char = length(cur_char);
                        end;
                    pulse_n_in_ch = floor(sys(2) / 4) + 1;
                  cur_byte = 4 - ceil(sys(2) / 6);
                        cur_char_byte = str2num(cur_char(cur_byte));
                    pulse_post_in_byte = ceil(sys(2)/2) - 3 * (3- cur_byte);
                        if pulse_post_in_byte == 1
                              sys(6) = rem(cur_char_byte, 2);
                 elseif pulse_post_in_byte == 2
                          if sys(2) == 15
                                 summ = 0;
                                       for i=1:3
                                               tmp = str2num(cur_char(i));
                                             summ = rem(tmp+floor(tmp/2)+floor(tmp/4),2) + summ;
                                     end;
                                    sys(6) = rem(summ,2);
                           else
                                    sys(6) = rem(floor(cur_char_byte/2), 2);
                                end;
                    else
                            sys(6) = rem(floor(cur_char_byte/4), 2);
                        end;
%line for check
%              [t, str2num(cur_char), cur_char_byte, pulse_post_in_byte, cur_byte, sys(2), sys(6)]
           end;
            %when never transfered before and received the transfer signal.
 end;
elseif flag == 3 %output calculation
        if x(1)==1
              sys = x(6);
     else
            sys = 0;
        end;
elseif flag == 4 %time calculation.
 if x(1) == 1
            sys = t + x(5);
 elseif x(1) == 0
                sys = t + period/8;
     else
            sys = Inf;
      end;
elseif flag == 0 %initial condition
 if ~isstr(source)
               [sys,tmp]=get_param;
            sys=['Problem in block ', sys,'/',tmp,'The block can convert string only.'];
            error(sys);
     end;
    sys = [0;6;1;1;0;0];
    x0 = [0;0;0;length(source(:));period/8;0]; 
                     %x(1) is enable triggle;
                        %x(2) is pulse counting;
                        %           4 points for a pulse, total 8 pulse for a character.
                        %x(3) is character counting.
                    %x(4) is the length of the source to be transfered.
                     %x(5) is the next time increament
                       %x(6) is the output to be.
      if period < width*8
        error('The periodic length must be at least eight times wider than pulse width');
    end;
    if u==1
         x0(1) = 1;
      end;
else
        sys = [];
end;