TDP databus is a custom developed protocol (tripping data protocol), that uses 4 data lines for a stabile communication. These lines are:

1. S_DO (Data out)
2. S_DI (Data in)
3. S_OKO (Data ok out)
4. S_OKI (Data ok in)

Note that, a master and slave are connected in the following way: (cross-over)

MASTER = SLAVE

S_DO = S_DI

S_DI = S_DO

S_OKO = S_OKI

S_OKI = S_OKO

The following image represents how a Master and a Slave are connected to a Data Bus. The purple line connecting Master and Slave is a selection line, that selects which Slave reads/writes data (in case of more than one slave).

Every communication is initiated by the Master.

The protocol is not time sensitive, since it uses S_OKO and S_OKI pin to drive data transfer. A new bit will not be sent until S_OKI data says that the previous bit was successfully received.

HERE's the code, if it can help you in any way, you are free to use it:

/*
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program.  If not, see <http://www.gnu.org/licenses/&gt;.

**********************************************************************
#include <16F627A.h>
#device ADC=16
#FUSES NOWDT                                           
#FUSES NOMCLR                                       
#FUSES NOBROWNOUT                            
#FUSES NOLVP                                           
#FUSES NOCPD, NOPROTECT, NOPUT, INTRC_IO

#use delay(internal=4MHz)
#use STANDARD_IO( A,B )

                                      
#define S_OKO PIN_A0
#define S_OKI PIN_A7   
#define S_DI PIN_A6
#define S_DO PIN_B7

int16 precalc_val[15] = { 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048, 4096, 8192, 16384 };

void ___outbit(int1 val)
{
   output_high(S_OKO);
   if(val == 1)
      output_high(S_DO);
   while(!input(S_OKI));
   output_low(S_OKO);
   while(!input(S_OKI));
   while(input(S_OKI));
   output_low(S_DO);
}

int1 ___inbit()
{
   int1 r = 0;
   if(!input(S_OKI))
      while(!input(S_OKI));
   
   delay_us(100);
   output_high(S_OKO);

   
   while(input(S_OKI));
   
   if(input(S_DI))
      r = 1;
      
   delay_us(100);
   output_low(S_OKO);
   delay_us(100);
   return r;
}

void TDP_init()
{
   output_low(S_OKO);
   output_low(S_DO);
   input(S_DI);
   input(S_OKI);
}

void TDP_Write(int16 data)
{
   int16 k, c;
   for (c = 14; c >= 0; c--)
   {
      k = data >> c;
 
      if (k & 1)
          ___outbit(0x01);
      else
          ___outbit(0x00);
      
      if (c == 0)
         break;
   }
}

int16 TDP_Read()
{
   int16 data = 0;
   int1 val = 0;
   
   for(int i = 14; i>= 0; i--)
   {
      val = ___inbit();
      if(val == 1)
         data += precalc_val[i];
      if (i == 0)
         break;
   }

   return data;
}