the "Jonas Sound Card"
      an interresting "alternative" to the Mockingboard		    Page No.:H213-2
 
         
     
 		  
   


  Here is a picture of the first circuitplan:
 

   

 In this design the card should offer the ability to be set with a small program to determine, if the card should pick up the sound from the IIGS soundport
 and just pass over that sounds straight to the output amplifier, or if the card should be driven by the 65C22 and the YM-2203 replacing the Mockingboard
 just having the additional capability to also get the YMZ-284 or the YM-3014 driven by the 65C22 and each of this chips equipped with the ability to be
 handling software compatible with a AY-3-8913 and passing that sounds to the audio output amplifier. This was realized by a CMOS audio switching chip
 4052 that permits to select in stereo mode a output-channel out of 4 input-channels by "softswitch" ( a specific set of softwareadresses selected and fed with 
 specific data bit-matrix and that byte stored in a latch until the pattern gets changed by next software access to the specific memoryadress.
 The selectionprogram for use of the softswitch setting the audiooutput with extended comments is here:
 

   
   
   
   
   
   
   

 and if just used with a fixed setup without choosing by menu the progam can be shorted drastically down to the example below:
 

   

 The commented programm with use of the menus selecting slot and operation mode takes 17 sectors,
 while the "short"version without selection menus as a kind of "pre-loader" just setting the card only uses 2 sectors.

 Anyhow the first design still had the  disadvantage that in some cases the YM-2203 and the YMZ-284 could start fighting about the use of the data
 on the bit port D0 to D7 from the WD65C22 VIA chips to the soundchips. This problem was eliminated in the second design by change of the source
 where the Chip-select signals have been taken from and by relocating one chipselect line to the input side of the inverting gate at the command decoding  
 circuitry. This causes in result that only one of both chips in the both channels, either the YM-2203, or the YMZ-284 would be selected and therefor gain
 for access to the datalines.

 That second version of the card is explained at the next page.

 
         
         
         
         
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