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> I cannot get S8 work no matter what. While running FFF1 sequence it is using 92mA current at 5V supply.

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OK, that's correct. You have enough 5v power.

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> While testing with the logic probe, 74LS145 inputs to A(15), B(14) and C(13) are fine but D(12) is always LOW.

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That's also correct. 74LS145 input D (pin 12) is always low when the interrupt handler is working. The inputs to it count from 0-7 and repeat. If the Z80 interrupt handler fails to respond to the keyboard/display interrupt, then input D (pin 12) goes high to disable the LED display and keypad.

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As I described earlier, you can test the Front Panel by itself, without the CPU board. You should be able to set the A B C inputs of the 74LS145 (with the 74HC393 counter) to each of the 8 states, then operate each keypad key in turn, and see the IN bits identify which key you pressed.

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Lee

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I am using the (b) TTL configuration both on the Z80 card as well as the Front panel.

--

Excellence does not require perfection. -- Henry James

But it *does* require attention to detail! -- Lee Hart

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Lee A. Hart