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Analyzing the vintage 8008 processor from die photos: its unusual counters
- sehugg 10y agoThe Atari 2600's TIA made use of these pseudorandom counters, too, for the current horizontal raster position of sprites and other objects. As a result, the programmer couldn't set the position directly -- you'd have to wait for the counter to reach the desired value, then strobe a register that sets the position register (to the opaque pseudorandom value). You could then nudge it -8 or +7 pixels with yet another register.
- jonsen 10y agoA Johnson counter is often used in similar circumstances. To count eight states 0000 -> 0001 -> 0011 -> 0111 -> 1111 -> 1110 -> 1100 -> 1000 -> 0000 it would have to be a four bit register ABCD where A = B, B = C, C = D, and D = NOT A It would be one more flip-flop but the counting logic would be free. A flip-flop has a NOT output. Decoding of the eight states are also simple: State 0000 is NOT A AND NOT D State 0001 is NOT C AND D and so on. Notice the NOTs are free.
- burntrelish1273 10y agoHere's the user manual in pdf form: http://www.classiccmp.org/8008/8008UM.pdf http://www.classiccmp.org/8008/8008UM.pdf