Getting there: finally I can see the hex result on the display after I
press the input button. Seems to me that the control circuit work fine.
However I tried to test the machine by entering 7b (SEQ) and pressed INPUT
and set to RUN mode, expecting the Q output change it's state. It didn't
happen:( The 1802the input and output section and the whole control circuit
seem to work fine so I checked the RAMs. It seems that the read/write
enable and output disable pins (18 and 20) show different logic state in
the two memory ICs. I assume this stops the instruction to be entered to
the memory. Can you guys tell me what should be the state of pins 18 and 20
(output disable and write enable) in run and load mode and when pressing
the input button? The datasheet doesn't have much info on this.
On 16 March 2012 18:15, Gergely L?rincz <alkopop79 at gmail.com> wrote:
Problem (partially) solved: the LOAD switch stops the
fliflop letting
anything pass through until it's set on ( RESET mode). As if someone
mentioned it that particular bit is wrong on the schematics. I assume i
just have to rewire the thing.
On 16 Mar 2012 00:51, "Gergely L?rincz" <alkopop79 at gmail.com> wrote:
> All of these test are done. Conclusion: if I remove the wire to SC1 and
> reset the 4013, it works fine, just as you described. In fact, I spent a
> few hours sending pulses from an Arduino (microsecond ones) to simulate
> SC1. I even managed to see the pulse from *Q* on the oscilloscope. But
> once the wire between the 4013 and the SC1 pin is used, nothing works. I
> even tried two different 1802s and they work fine (when the DMA IN pin is
> set low, SC1 instantly goes high). The only possible reason I can think of
> (since both the 1802 and 4013 works perfectly) is that one of the diodes
> are either broken or placed the wrong way around. An other thing is that I
> use a SPST button (input) instead of the SPDT. It still works (for some
> weird reason no SPDT buttons are rare and expensive in the UK). I'll check
> this tomorrow. The other mystery is that why the 4023 never sets the HP
> displays to enable mode. The displays are stuck (latched) and even though
> they work perfectly, the NAND gate (4023) never sets the enable pins low. I
> wonder if that has to anything with the previous problem? Anyway, at least
> I know where the problem is, even though I don't know what it is. It's
> certainly a good start! Thanks for all of your effort and indispensable
> help!
>
> Greg
>
>
>
>>
>> Debugging trial: remove the connection from SC1 to the diode at the 4013
>> reset (10).
>> Now, when the input switch is released, nQ & nDMAIN should go low and
>> STAY low as there is nothing to reset the 4013 (until you flip the load
>> mode switch).
>> It follows SC1 should go high and stay high or repeatedly pulse high as
>> the 1802 is being held in the DMA state (which I think you already tested
>> by forcing nDMAIN low).
>>
>>
>>
>>
>>
>