I've been attempting to program a few different micro-controllers using nothing but an FTDI 5V TTL cable and self-written software to bitbang the needed pins on the chips. Until now I had success only with my AT89S52 chips but I have a similar problem with the rest. The rest being an ATmega8, ATtiny13 and even a PIC16F84A.
None of these chips seems to respond on the appropriate pins (MISO, SDO, etc) while programming. These pins seems to always be in an high-impedance state and doesn't get pulled either HIGH or LOW.
I've checked this with a simple LED "logic probe", my Arduino as a Logic Analyzer, oscilloscope. There's just no response from these chips.
I even tried programming from the Arduino with simple sketches (SPI or bitbang) with exactly the same effect.
Is there something I'm missing or obviously doing wrong?
For all micro-controllers I've connected the pins directly to the FTDI cable's wires (or Arduino's pins) and in case HV programming is required I used the following circuit (which seems to work just fine when I'm measuring with my multimeter):
simulate this circuit – Schematic created using CircuitLab
Best Answer
One possibility is that the chips you're trying to program are expecting an external oscillator instead of using their internal RC oscillators. I know when I first programmed an AVR I had the fuses set wrong, so to be able to program it again I needed to add an external oscillator.