making a Apple-1 diagnostic card
 "on the draft"
   Page No.:A18

   While building up a replication of the Apple-1 the user might face a problem:
   when the board is powered up and all solderingjoints look perfect by inspection and powerlines show the defined voltages and a
   inspection of the timingsignals with an oscilloscope show the correct rectangle wave the system srill might refude to boot correct
   to the prompt.

   In such a case itīs not allways usefull to inspect the total system with a oscilloscope - due to the fact that the sxpected signals might be
   viewable but not working in the correct condition.... In such a case it is more usefull to make a diagnosticcard and bringup the display of
   all signals availiable at the system....  this will enable to detect if a adressingline or adataline is hooked up at a specific adress while bootup
   is performed or if for example a controling line like thge reset or NMI is blocking the startup of the system....
   Within the Apple-1 manual there is at page 12 a circuitplan proposed as "adressingdisplay". But this plan only brings up the display of
   the adressinglines and the datalines as well as the controllines and clockinglines canīt be view with that proposal. At the other hand at
   the same pageof the Apple-1 manual there is also a proposal how to make a stepping logic for single steps or cycles at the system...
   this proposal is quite interesting for debugging programms ..... At the other hand that page does not make nay proposal about a "reset"-
   button or any kind of use of the NMI-line.

   I have therefor made a card with a combination to display all signals availiable at the slot : adressinglines, datalines, controllines and
   clockinglines as well as the so called selectionlines R, S and T which will be used for selecting expansioncards and generated by the
   74154 at the center of the replicationboards and responsible for the hardcoded adressing of the adressing space of the replication as
   well as also containing the stepping logic for debugging and offering a resetbutton and a button to access also the NMI-line.

   Another aspect of the card is that like in the original proposal the card shall "latch" the display. This is by explenation "a kind of static
   picture" of the conditions at the signalbus. But for degugging process itīs more usefull to view in general the "dynamic" process at the
   signalbus. Therefor the card contains a switch (S6) that permits to decide in which kind of "mode" the display shall operate. That permits the
   user to decide if he wants to track the dynamic operation of the system and accepting that some signals are that fast that a user canīt
   watch the fast transitions of the signals but recognize the operation or if the user wantīs to take a single "timeshot" of the conditions....

   To tell the truth - itīs mnot completely "invisible" if transitions are performed at the signallines.... in fact if fast transitions occur at the
   signallines it just looks like the LEDs get "dimmed" while static lines without change will remain at full brightness of light if siganl is
   at "high" state or total darkness if the signal stays at "low" state.

   Due to the fact that at the expansionbus there are 44 connections - of only 5 lines contain power and the remaining 39 lines are related
   to signals it is recommended to use the 74373 as "latch" instead of the 74174. the 74174 only latches 6 lines ( resulting to the need of
   7 ICs for the 39 signals ) while the 74373 latches 8 lines and only 5 ICs will be requested. Another aspect will be the use of power....
   using normal single LED with each requesting 20 mA for emmiting light would make summary of 780 mA not adding the internal use
   of the ICs .... itīs therefor recommended to use instead so called LED-bars .... that LED often only request 12 mA for full lighting up and
   therefor will drop the demands to the powersuply from 780 mA down to 468 mA cutting the requested use of power by 40%.


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