Path: blue.weeg.uiowa.edu!news.uiowa.edu!uunet!munnari.oz.au!yoyo.aarnet.edu.au!news.adelaide.edu.au!gateway.dircsa.org.au!cleese.apana.org.au!cleese.apana.org.au!not-for-mail From: ntt@cleese.apana.org.au (Jonathan Pratt) Newsgroups: comp.sys.apple2 Subject: Re: Wishing to build a stereo card Date: 4 Aug 1994 12:50:15 +0930 Organization: cleese.apana.org.au Public Access UNIX +61-8-3736006 Lines: 43 Distribution: world Message-ID: <31pmpf$d5k@cleese.apana.org.au> References: <31kg71$pce@master.cs.rose-hulman.edu> NNTP-Posting-Host: cleese.apana.org.au There is a 7-pin molex connector near the memory expansion slot on the GS. This is the sound input/output port for the GS and is used by all cards which make use of the GS Ensoniq DOC for stereo, but can potentially drive 8-channel outputs. Each oscillator has a control register with bits 4-7 defining the channel adress, although bit 7 is not supported by hardware (ie 8 channels only). The control register serves other functions also, as described in the GS hardware reference. The molex connector has pins as described... 1 A/D converter input 2 Analogue GND 3 Analogue output (-5V to 5V) 4 Channel Address 0 5 Channel Address 1 6 Channel Strobe 7 Channel Address 2 The channel strobe goes low when there is a valid address on the Channel Address, which can be demultiplexed to give 8 channel outputs. The voltage level from the analogue out needs to be passed to the appropriate channel amp (simple op amp stage) and maintained until that address is updated. Stereo works by using CA0 only and ignoring CA1 and CA2, although this would sound awful if anyone wrote a program which made use of the other six channels (ie programmed the oscillator control registers to use channels 2 to 7) This is not a difficult project, and the hardware reference give a simple circuit description for making use of the outputs. No slot is required to make this work (ie slot independant) but the circuitry can make use of the power rails of a slot (+/-12V, +/-5V, GND) to drive the IC's. Hence cards like the SoundMeister are slot independant except for altering some of the extra features you may wish to include. eg Digital delay, chorus, reverb, noise suppression, or sensitivity of a digitizing circuit (which can make use of the DOC which has a built in A/D converter). Cheers ntt@cleese