Twisting wires together doesn't cancel interference unless those two wires carry equal-but-opposite signals that are fed to a balanced input. AFAIK, it can only hurt as the signals may then couple to each other.
Also, I would refactor your module like so:
char data[8]; // Forget _d0-_d7
uint8_t Maxim6955::write(uint8_t chr) {
Wire.beginTransmission(_address);
Wire.write(0x20);
// Shift values back one digit, writing along the way to save a second loop
for (uint8_t i = 1; i < 8; i++) {
Wire.write(data[i]);
data[i-1] = data[i];
}
// Shift in new char and write it
data[7] = chr;
Wire.write(chr);
Wire.endTransmission();
// Return an error code if you have one...
return (TWI_error_code);
}
// Print C-style strings
uint8_t Max6955::print(char *str) {
uint8_t i = 0;
uint8_t ret;
// Loop through C-style string and write each char
while (str[i] != 0x00) {
ret = write(str[i]);
if (ret != 0) break;
}
// Pass along any errors
return ret;
}
// Overload print for C++ strings
uint8_t Max6955::print(String str) {
// Loop through string chars one at a time, calling write(char) for each
// Return error code from write(char) if != 0
}
// You may wish to overload print for ints, floats, etc. Up to you.
// Call print with 8 spaces
uint8_t Max6955::clear() {
return print(" ");
}
I'm a C guy, so I'm not totally up to speed on C++ .. at least, the finer details of classes. I'm halfway through a book, but not ready to write my own code here, so you'll have to fill in the details on the C++ String handling, and any errors I made on calling conventions within a namespace.