PIC "Begin Erase/End Programming" question

Rusttree said:

The 14 bits are padded on either side, making the whole "word" 16 bits long. According to the prog spec, after issuing a Read Data or Load Data command, the clock is cycled 16 times, with the first and last bits being "start" and "stop" bits.

I noticed that when reading a word in memory, the PIC always throws a "1" as the 1st bit and another "1" as the 16th bit. The 14-bit word I programmed is between those two 1's. When the MSB of my 14-bit word is a "0", it doesn't throw the "1" as the 16th bit. And everything after that fails to read.

I did confirm that the PIC is being programmed correctly by incrementing passed the troublesome word and continuing to read.

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Procedure OutWord(Data : Word);
Var
  x,
  BitPos : Word;
Begin
  ClockPulse(DLow);
  BitPos := 1;
  For x := 0 To 13 Do
  Begin
    IF (Data AND BitPos) = BitPos THEN
      ClockPulse(DHigh)
    ELSE
      ClockPulse(DLow);
    BitPos := BitPos Shl 1;
  End;
  ClockPulse(DLow);
End;

Rusttree said:

I guess I'm using the 16-bit mentality because that's how the hex file is constructed. They're all 16-bit values with 0's always as the first and last bit.

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Rusttree said:

Well, you inadvertantly solved my problem. By having the logic treat the read as a 16-bit value instead of a 14-bit value with 2 extra clock cycles, I wasn't paying close enough attention to the 1st and 16th clock cycle during the read. After I rewrote my code, I realized the data pin was being inappropriately latched during the clock cycle. Still not 100% sure why that caused the problem, but by forcing the data pin low during the 1st and 16th clock cycles, it solved my problem.

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