function [PencilData, PencilHeader, PencilSwitches] = readpencil(fname, verbose)
% READPENCIL - read in data from Imagenex pencil beam sonar
% [PencilData, PencilHeader, PencilSwitches] = readpencil(fname, verbose);
% 
% fname = file name
%
% PencilData.imagedata: [ping x bin double], image data with header removed
% 
% HeaderData is a dump of the header info sent with *each ping*
% HeaderData.ReturnDataHeaderType = IGX/IMX etc.
% HeaderData.HeadID = ID number
% HeaderData.HeadPosition = head position in counts
% HeaderData.HeadAngle = head rotation angle in degrees
% HeaderData.StepDirection = direction of rotation, -1 = CCW, 1 = CW
% HeaderData.Range = range setting
% HeaderData.ProfileRange = first digitized value above the threshold in cm
% HeaderData.NDataBytes = number of byte in the ping
% HeaderData.NReturnBytes = number of bytes in the ping + header
% HeaderData.StepSize = degrees per step of rotation
% HeaderData.FileName = name of the file read
% HeaderData.NPoints = number of data points returned for the ping
% HeaderData.SectorWidth = size of sector swept in degrees
% HeaderData.StartGain = gain setting word from switches (for .81a files)
%
% PencilSwitches is a dump of the switches sent to the sonar for this sweep
% PencilSwitches = 
%          HeadID: 16
%           Range: 2
%        Reserved: [0 0 0 0 0 0]
%         RevHold: 'Reverse Step Direction'
%     MasterSlave: 'Send Data Slave Mode'
%       StartGain: 5
%            LOGF: 20
%      Absorption: 0.0600
%      TrainAngle: 0
%     SectorWidth: 150
%        StepSize: 0.3000
%     PulseLength: 10
%      DataPoints: 500
%        DataBits: 8
%          UpBaud: 6
%         Profile: 'OFF'
%       Calibrate: 'Calibrate'
%     SwitchDelay: 2
%       Frequency: 900

% 16jul07 fix bad bit parsing of Profile Range and NDataBytes in header
% Written by Marinna Martini 5/22/07
% for the U.S. Geological Survey, WOods Hole Field Center
%
% 07/06/07 ETM- made all StepSize == 0.3 pre conv. with Doug Wilson
%  and made a case to exit cleanly if  all header words are 0

NRETURNHEADERBYTES = 12;
NWHSCFILEHEADERBYTES = 61;
N81AFILEHEADERBYTES = 100;
PencilData = [];
PencilHeader = [];
PencilSwitches = [];

if ~exist('fname', 'var') || ~exist(fname, 'file'),
    [fname, pathname] = uigetfile( ...
       {'*.P*','WHSC logger files (S1*.P*)'; ...
        '*.81A','Win8812W output files (*.81A)'; ...
        '*.*',  'All Files (*.*)'});
    if isempty(fname), return, end
    fname = fullfile(pathname, fname);
end
fid = fopen(fname,'r');
if fid == -1,
    disp(['error reading file ',fname]);
    return
else
    disp(['Now reading file ', fname]);
end
PencilHeader.FileName = fname;

if ~exist('verbose','var'),
    verbose = 1;
end

% detect which file we have
% read the first few bytes
tag = fread(fid,3,'uchar');
fseek(fid,0,'bof');

switch(char(tag)')
    case 'The' % this is USGS WHSC logger data
        % extract year info from file
        d = dir(fname);
        datayear = datevec(d.datenum);
        % first part is the file name, as written by the logger,
        % which is essentially the time stamp
        fheader = fread(fid,NWHSCFILEHEADERBYTES,'uchar');
        [PencilTime, PencilSwitches] = parseLoggerHeader(fheader, datayear(1));
        clear d
        
        % now at the data
        % decipher the first 13 bytes of sonar header so we know what we are reading
        sheader = fread(fid,NRETURNHEADERBYTES,'uchar');
        header = parsePencilheader(sheader, PencilSwitches, verbose); % display them once
            if isempty(header)  %handles the empty header case
                return
            end
        disp(sprintf('Number of return bytes per ping = %d',header.NReturnBytes));
        npoints = header.NReturnBytes-NRETURNHEADERBYTES+1;
        disp(sprintf('Number of points per ping = %d',npoints));
        PencilHeader.PencilTime = PencilTime; % pass out the time stamp
        clear sheader

        % now figure out how many pings of data are in this file from the file size and header info.
        fileinfo = dir(fname);
        disp(fileinfo.bytes);
        npings = (fileinfo.bytes-NWHSCFILEHEADERBYTES)./header.NReturnBytes;
        disp(sprintf('Number of pings in the file = %d',npings))

        fseek(fid, NWHSCFILEHEADERBYTES, 'bof'); % go to data start
        raw = fread(fid,'uchar'); % read in all the ping data
        endval=header.NReturnBytes*floor(npings);
        imagedata = reshape(raw(1:endval), header.NReturnBytes, floor(npings));

        % let's check out the header for each ping
        for iping = 1:npings,
            header = parsePencilheader(imagedata(1:13,iping), PencilSwitches, 0);
            % rearrange the output for convenience
            PencilHeader.ReturnDataHeaderType{iping} = header.ReturnDataHeaderType;
            PencilHeader.HeadID(iping) = header.HeadID;
            PencilHeader.HeadPosition(iping) = header.HeadPosition;
            PencilHeader.HeadAngle(iping) = header.HeadAngle;
            PencilHeader.StepDirection(iping) = header.StepDirection;
            PencilHeader.Range(iping) = header.Range;
            PencilHeader.ProfileRange(iping) = header.ProfileRange;
            PencilHeader.NDataBytes(iping) = header.NDataBytes;
            PencilHeader.NReturnBytes(iping) = header.NReturnBytes;
        end

        PencilData.imagedata = imagedata(14:end,:); % pass back just data
        PencilHeader.NPoints = PencilSwitches.DataPoints;
        PencilHeader.StepSize = PencilSwitches.StepSize;
        PencilHeader.SectorWidth = PencilSwitches.SectorWidth;

    case '81A' % this is data from an 81A file
        fheader = fread(fid,N81AFILEHEADERBYTES,'uchar');
        [PencilTime, PencilSwitches] = parse81AHeader(fheader,1);
        
        % now at the data
        % decipher the first 13 bytes of sonar header so we know what we are reading
        sheader = fread(fid,NRETURNHEADERBYTES,'uchar');
        header = parsePencilheader(sheader, PencilSwitches, verbose); % display them once
        PencilHeader.FileName = fname;
        PencilHeader.NPoints = header.NDataBytes;
        PencilHeader.StepSize = PencilSwitches.StepSize;
        PencilHeader.SectorWidth = PencilSwitches.SectorSize;
        clear sheader
        
        % now figure out how many pings of data are in this file from the file size and header info.
        fileinfo = dir(fname);
        disp(sprintf('The file size is %d',fileinfo.bytes));
        npings = (fileinfo.bytes)./(PencilSwitches.TotalBytes);
        disp(sprintf('Number of pings in the file = %d',npings))
        
        % allocate memory
        fseek(fid, 0, 'bof'); % go to data start
        
        raw = fread(fid,'uchar'); % read in all the ping data at once
        imagedata = reshape(raw, PencilSwitches.TotalBytes, npings);
        PencilData.raw = imagedata;

        % let's check out the header for each ping
        for iping = 1:npings,
            [PencilTime, switches] = parse81AHeader(imagedata(1:100,iping),0);
            PencilHeader.PencilTime(iping) = PencilTime;
            header = parsePencilheader(imagedata(101:112,iping), PencilSwitches, 0);
            if ~isempty(header),
                % rearrange the output for convenience
                PencilHeader.ReturnDataHeaderType{iping} = header.ReturnDataHeaderType;
                PencilHeader.HeadID(iping) = header.HeadID;
                PencilHeader.HeadPosition(iping) = header.HeadPosition;
                PencilHeader.HeadAngle(iping) = header.HeadAngle;
                PencilHeader.StepDirection(iping) = header.StepDirection;
                PencilHeader.Range(iping) = header.Range;
                PencilHeader.ProfileRange(iping) = header.ProfileRange;
                PencilHeader.NDataBytes(iping) = header.NDataBytes;
                % this only works for .81a files-  
                % logger generated .P## and .R## files only do switches once
                PencilHeader.StartGain(iping) = switches.StartGain;
                if ~isempty(header.NReturnBytes), PencilHeader.NReturnBytes(iping) = header.NReturnBytes;
                else PencilHeader.NReturnBytes(iping) = NaN;
                    disp(sprintf('Problem at ping #%d',iping))
                end
            else
                disp(sprintf('Problem at ping #%d',iping))
            end
        end

        PencilData.imagedata = imagedata(113:end,:); % pass back just data

        case {'IGX','IMX','IPX'} % .81a is also an IMX, so was read twice
   % case {'IGX','IMX','IPX'} % this is USGS WHSC logger *.tmp format
        % extract year info from file
        d = dir(fname);
        PencilTime = julian(datevec(d.datenum));
        PencilHeader.PencilTime = PencilTime; % pass out the time stamp
        
        % need to know the data bits, 4, 8 or 16!
        button = questdlg('Select number of Data Bits','No SwitchInformation','4','8','16','8');
        PencilSwitches.DataBits = str2num(char(button));

        % this file format has no header, it goes right to the data
        % decipher the first 13 bytes of sonar header so we know what we are reading
        sheader = fread(fid,NRETURNHEADERBYTES,'uchar');
        header = parsePencilheader(sheader, PencilSwitches, verbose); % display them once
        disp(sprintf('Number of return bytes per ping = %d',header.NReturnBytes));
        npoints = header.NReturnBytes-NRETURNHEADERBYTES+1;
        disp(sprintf('Number of points per ping = %d',npoints));
        clear sheader

        % now figure out how many pings of data are in this file from the file size and header info.
        fileinfo = dir(fname);
        disp(fileinfo.bytes);
        npings = (fileinfo.bytes)./header.NReturnBytes;
        disp(sprintf('Number of pings in the file = %d',npings))

        fseek(fid, 0, 'bof'); % go to data start
        raw = fread(fid,'uchar'); % read in all the ping data
        imagedata = reshape(raw, header.NReturnBytes, npings);

        % let's check out the header for each ping
        for iping = 1:npings,
            header = parsePencilheader(imagedata(1:13,iping), PencilSwitches, 0);
            % rearrange the output for convenience
            PencilHeader.ReturnDataHeaderType{iping} = header.ReturnDataHeaderType;
            PencilHeader.HeadID(iping) = header.HeadID;
            PencilHeader.HeadPosition(iping) = header.HeadPosition;
            PencilHeader.HeadAngle(iping) = header.HeadAngle;
            PencilHeader.StepDirection(iping) = header.StepDirection;
            PencilHeader.Range(iping) = header.Range;
            PencilHeader.ProfileRange(iping) = header.ProfileRange;
            PencilHeader.NDataBytes(iping) = header.NDataBytes;
            PencilHeader.NReturnBytes(iping) = header.NReturnBytes;
        end

        PencilData.imagedata = imagedata(14:end,:); % pass back just data
        PencilHeader.NPoints =  header.NReturnBytes-NRETURNHEADERBYTES+1;
        %PencilHeader.StepSize = PencilSwitches.StepSize;
        %PencilHeader.SectorWidth = PencilSwitches.SectorWidth;
        
    otherwise
        disp('Data is unrecognized')
        return
end

fclose(fid);

return

PencilSwitches = parsePencilswitches(fheader(35:end));

% now at the data
% decipher the first 13 bytes of sonar header so we know what we are reading
sheader = fread(fid,NRETURNHEADERBYTES,'uchar');
PencilHeader = parsePencilheader(sheader, PencilSwitches, verbose); % display them once
disp(sprintf('Number of return bytes per ping = %d',PencilHeader.NReturnBytes));
npoints = PencilHeader.NReturnBytes - NRETURNHEADERBYTES;
disp(sprintf('Number of points per ping = %d',npoints));
PencilHeader.PencilTime = PencilTime; % pass out the time stamp
clear sheader

% now figure out how many pings of data are in this file from the file size and header info.
fileinfo = dir(fname);
disp(fileinfo.bytes);
npings = (fileinfo.bytes-NFILEHEADERBYTES)./PencilHeader.NReturnBytes;
disp(sprintf('Number of useable pings = %d',npings))

% Marinna reads the data
fseek(fid, NFILEHEADERBYTES, 'bof'); % go to data start
A1 = fread(fid,'uchar'); % read in all the ping data
imagedata = reshape(A1, PencilHeader.NReturnBytes, npings);
fclose(fid);

PencilData.rawimage = imagedata; % pass back unadulterated data to play with

% let's check out the header for each ping
clear PencilHeader
for iping = 1:npings,
    PencilHeader(iping) = parsePencilheader(imagedata(1:13,iping), PencilSwitches, 0);
end

return

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% read a WHSC logger file header from a S1*.F* file
%
function [PencilTime, PencilSwitches] = parseLoggerHeader(fheader, datayear)

% bytes 1:33 are:
% The file name is \S1\S1031414.p12
% it is possible that this can vary
% extract the time information from the file header
cfheader = char(fheader);
MM = sscanf(cfheader(24:25),'%d');
dd = sscanf(cfheader(26:27),'%d');
hh = sscanf(cfheader(28:29),'%d');
mm = sscanf(cfheader(32:33),'%d');
PencilTime = julian([datayear, MM, dd, hh, mm, 0]);
clear MM dd hh mm cfheader
% next thing the logger writes out are the switches.  29 bytes.
% not sure why byte #34 is written.  It is ASCII LF = x0A
% pull out switch data for indexing convenience
PencilSwitches = parsePencilswitches(fheader(35:end));

return

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% read the header from an output file from live operations (win881A.exe)
function [PencilTime, File81AHeader] = parse81AHeader(fheader, verbose)

File81AHeader.ReturnDataHeaderType = char(fheader(1:3))';
junk = [0 128 250 500];
File81AHeader.NDataBytes = junk(fheader(4)+1);
File81AHeader.TotalBytes = fheader(5).*256+fheader(6);
File81AHeader.nToRead = fheader(7).*256+fheader(8);
% date format 11-May-2007.21:30:05
dstr = char(fheader(9:29)');
dstr(12) = ' ';
hsec = str2num(char(fheader(31:32))); % byte 30 is '.' and byte 33 is null
PencilTime = julian(datevec(datenum(dstr)));
File81AHeader.xBytes = fheader(35).*128;
File81AHeader.TotalBytes = File81AHeader.TotalBytes + File81AHeader.xBytes;
File81AHeader.StepDirection = bitget(fheader(38),8); % 1 = CW
File81AHeader.Orientation = bitget(fheader(38),7); % 1 = Up
junk = {'Sector','Polar','Sidescan'};
n = bitshift(bitand(fheader(38), 56),-3); 
File81AHeader.Mode = junk{n+1};
% junk = [0 0.3 0.6 0.9 1.2 2.4];
junk = [0.3 0.6 0.9 1.2 2.4];  % can't use the leading 0
File81AHeader.StepSize = junk(bitand(fheader(38), 7)+1);
% StepSize is ALWAYS .3 for Pencil- Doug Wilson, Pers.Comm 6/07
% File81AHeader.StepSize = 0.3;
File81AHeader.StartGain = fheader(39);
File81AHeader.SectorSize = fheader(40).*3;
% I don't think this should be -210  etm
% File81AHeader.TrainAngle = (fheader(41).*3) - 210;
File81AHeader.TrainAngle = (fheader(41).*3);
File81AHeader.RangeOffset = fheader(42);
File81AHeader.Absorption = fheader(43).*0.01;
File81AHeader.ProfileGrid = bitget(fheader(44),8); % 1 = ON
File81AHeader.Zero = bitget(fheader(44),7); % 1 = Dn
junk = [4 8 14];
n = bitshift(bitand(fheader(44), 56),-3);
File81AHeader.DataBits = junk(n+1);
File81AHeader.LogF = bitand(fheader(44), 7).*10; 
File81AHeader.PulseLength = fheader(45).*10;
junk = {'Off','PointsOnly','Lo-mix','Hi-Mix'};
File81AHeader.Profile = junk{fheader(46)+1};
if bitget(fheader(47),8),
    File81AHeader.SoundVelocity = (bitand(fheader(46),127).*256+fheader(47))/10;
else  File81AHeader.SoundVelocity = 1500;
end
File81AHeader.Comment = fheader(49:80);
File81AHeader.OperatingFrequency = fheader(81).*256+fheader(82);
if bitget(fheader(83),8),
    File81AHeader.AzimuthDrivePosition = (bitand(fheader(83),127).*256+fheader(84));
else  File81AHeader.AzimuthDrivePosition = NaN;
end

if verbose,
    disp(File81AHeader)
end

return

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% read the header that comes with each ping.
% applies to logger and live data
function PencilHeader = parsePencilheader(sheader, switches, verbose)

%check that the header has something in it (etm 7/6/07)
   xx=find(sheader==0);
   if (length(xx)==length(sheader))
       display('header is all zeros- cannot process- exiting readpencil');
       PencilHeader = [];
       return;
   end
   clear xx

   %now start parsing the header
PencilHeader.ReturnDataHeaderType = char(sheader(1:3))';
PencilHeader.HeadID = sheader(4);
b=dec2base(sheader(5),2,8); % get the bits
if b(7),  PencilHeader.SerialStatus = 'Switches Accepted'; end
if b(8),  PencilHeader.SerialStatus = 'Character Overrun'; end
% head position
% explicitly the method from the Imagenex manual Yuk!
% HI = bitand(sheader(7),hex2dec('3E'));
% HI = bitshift(HI,-1); % shift right
% LO1 = bitand(sheader(7),hex2dec('01'));
% LO1 = bitshift(LO1,7);
% LO2 = bitand(sheader(6),hex2dec('7F'));
% LO = bitor(LO1, LO2);
% HI = bitshift(HI,8);
% HP = bitor(HI, LO);
% dec2bin(HP)
%  PencilHeader.HeadAngle = (HP-600)*0.3;
% disp(sprintf('IMagenex method head angle %f', PencilHeader.HeadAngle))
% Doug Wilson's method is more concise.  He probably didn't write the manual
 PencilHeader.HeadPosition = bitand(63,sheader(7)).*128 + bitand(127,sheader(6));
 PencilHeader.HeadAngle = ( PencilHeader.HeadPosition-600).*0.3; % degrees
 %PencilHeader.HeadAngle = ( PencilHeader.HeadPosition-600).*switches.StepSize; % degrees
if bitget(sheader(7),6),  PencilHeader.StepDirection = 1;
else PencilHeader.StepDirection = -1;
end
PencilHeader.Range = sheader(8); % meters
% MM 10jul07 
%PencilHeader.ProfileRange = bitand(127,sheader(10)).*127 + bitand(127,sheader(9)); % meters
% bitshift(A, k) % negative = shift right
PRHB = bitshift(bitand(sheader(10), 126), -1);
PRLB = bitor(bitshift(bitand(sheader(10), 1), 7),bitand(sheader(9), 127));
PencilHeader.ProfileRange = bitor(bitshift(PRHB,8),PRLB);
%PencilHeader.NDataBytes = bitand(127,sheader(12)).*127 + bitand(127,sheader(11)); % meters
PRHB = bitshift(bitand(sheader(12), 126), -1);
PRLB = bitor(bitshift(bitand(sheader(12), 1), 7),bitand(sheader(11), 127));
PencilHeader.NDataBytes = bitor(bitshift(PRHB,8),PRLB);
% given the header info, figure out how many data point we're dealing with
% the number of data bits is hardwired to 8 in the logger source code (new_bits)
PencilHeader.NReturnBytes = [];
PencilHeader.NZeroFillBytes = [];
switch(PencilHeader.ReturnDataHeaderType),
    case {'IMX'},   % switch data command for data points = 25
        if switches.DataBits == 4, % 128 Data Byes, 256 Points
            PencilHeader.NReturnBytes = 141; 
            PencilHeader.NPoints = 256;
        elseif switches.DataBits == 8, % 252 Data Byes, 252 Points
            PencilHeader.NReturnBytes = 265; 
            PencilHeader.NPoints = 252;
            PencilHeader.NZeroFillBytes = 19;
        elseif switches.DataBits == 16, % 500 Data Byes, 250 Points
            PencilHeader.NReturnBytes = 513; 
            PencilHeader.NPoints = 250;
        end 
    case {'IGX'},   % switch data command for data points = 50
        if switches.DataBits == 4,
            PencilHeader.NReturnBytes = 265; % 252 Data Byes, 504 Points
            PencilHeader.NPoints = 504;
        elseif switches.DataBits == 8,
            PencilHeader.NReturnBytes = 513; % 500 Data Byes, 500 Points
            PencilHeader.NPoints = 500;
            PencilHeader.NZeroFillBytes = 27; 
        else % 500 Data Bytes, 250 Points
            PencilHeader.NReturnBytes = 500; 
            PencilHeader.NPoints = 250;            
        end
    case {'IQX'},
        % there is no IQX for the pencil beam sonar
    case {'IPX'},  % Profile = ON
        PencilHeader.NReturnBytes = 13;  % 0 Data Byes, 0 Points
        PencilHeader.NZeroFillBytes = 15;
        PencilHeader.NPoints = 0;
    otherwise
        sprintf([PencilHeader.ReturnDataHeaderType,' not recognized'])
        return
end
if verbose,
    disp(PencilHeader)
end

return

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% this function is only used for logger acquired files- not .8a1's
% read the settings sent to the sonar head
% these are saved at the beginning of each data file in the logger
function switches = parsePencilswitches(switchdata)

% first two bytes are switch data header ID = 0xFE44
if (switchdata(1) ~= 254) || (switchdata(2) ~= 68),
    disp('Switch data header ID not found')
end
switches.HeadID = switchdata(3);
switches.Range = switchdata(4); % 5 to 255 m in 5 m increments
switches.Reserved(1) = switchdata(5); % always 0
b=dec2base(switchdata(6),2,8); % get the bits
if b(1), switches.RevHold = 'Hold Head';
else switches.RevHold = 'Resume';
end
if b(7), switches.RevHold = 'Reverse Step Direction';
else switches.RevHold = 'Normal Operation';
end
b=dec2base(switchdata(7),2,8); % get the bits
% I'm not too sure how to interpret the manual on this one
% but this should not matter to logger data
if b(1),
    if b(7), switches.MasterSlave = 'Transmit Slave Mode';
    else switches.MasterSlave = 'Transmit Master Mode';
    end
end
if b(2),
    if b(7), switches.MasterSlave = 'Send Data Slave Mode';
    else switches.MasterSlave = 'Send Data Master Mode';
    end
end
switches.Reserved(2) = switchdata(8); % always 0
switches.StartGain = switchdata(9); % 0 to 40dB in 1 dB increments
switches.LOGF = switchdata(10).*10; % in dB
switches.Absorption = switchdata(11)./100; % dB/m
if switches.Absorption == 253,
    disp('Absorption value of 253 detected, this is not allowed')
end
% the .3 is ALWAYS StepSize and 
 switches.TrainAngle = (switchdata(12).*3)-180; % degrees
 switches.SectorWidth = switchdata(13).*3; % degrees
 % pencil beam step increments are usually 0.3 degrees
  switches.StepSize = switchdata(14).*0.3; % degrees per step up to 2.4 
if switches.StepSize > 2.4,
    disp('Step size greater than 2.4 detected, this is not possible')
end
switches.PulseLength = switchdata(15).*10; % microseconds
switches.ProfileMinRange = switchdata(16)./10; % meters
switches.Reserved(3:5) = switchdata(17:19); % always 0
switches.DataPoints = switchdata(20).*10; % 250 for IMX and 500 for IGX
% resolution of data as data width...
% 4 bits = 2 data points per byte
% 8 bits = 1 data point per byte
% 16 bits = 2 bytes per data point
switches.DataBits = switchdata(21); % in bits
switches.UpBaud = switchdata(22); % not yet used
if switchdata(23), switches.Profile = 'ON';
else switches.Profile = 'OFF'; % return data will have IPX header
end
if switchdata(24), switches.Calibrate = 'Normal Operation';
else switches.Calibrate = 'Calibrate'; % head is moved to 0 degrees
end
% the delay to give a control program time to serially upload data
switches.SwitchDelay = switchdata(25).*2; % milliseconds 
if switches.SwitchDelay == 253,
    disp('Switch Delay value of 253 detected, this is not allowed')
end
switches.Reserved(7) = NaN;
switches.Frequency = ((switchdata(26)-100).*5)+675; % kHz
% termination byte
if (switchdata(27) ~= 253),
    disp('Switch data termination byte not found')
end
disp(switches)
return