The Tandy Speech/Sound Cartridge (SSC) is an interesting device made for the Color Computer 2 in 1984. The SSC's functions are: 1) convert text into speech, 2) play 3-part musical harmony, 3) create complex sound effects, 4) create speech via an allophone table. The SSC has 8 speech and 8 sound storage buffers. The hardware is based on General Instrument Corporation's GI PIC 7040-510 chip set: PIC 7040, AY3-8913, SP0256-AL2.

I don't intend to review the device as it is no longer in production. The thrust of this article is how to make the device work with OS-9 Level II. Let's start with some history. The Coco2 had available OS-9 Level I v.2. This software ran at 0.89MHz and expected at most 64K RAM.

The design of the SSC incorporates the above parameters. It expects a clock signal (Q) of 0,89MHz which is doubled internally to 1.79MHz and used by the sound effects chip. If the Coco clock is set to 1.79MHz (fast mode), all sounds and tones go up one octave although speech is not affected. The SSC also requires a -6v DC source for it's operational amplifiers. This is created by feeding the Coco E-clock line to a coil and rectifying the output. The circuit used fails at 2MHz because insufficient negative voltage is produced to run the amplifiers.

Connect a 470pF ceramic capacitor across the leads of R16. This capacitor value works on my unit. Check the output of the negative supply at both 1MHz and 2MHz. Look for minimal change from -6v at both 1 and 2MHz. Use a value that gets +-1v of the target value. This modifies the negative power supply for 2MHz operation. (This feed forward capacitor corrects the role off of the transitor used in the circuit. It is the simplest possible fix. RG 1999)

Connect a single throw double pole switch with the common lead going to the circuit board feed-through as indicated in the diagram. Pole A can go to IC3 pin 8 and pole B to pin 9. Mark the switch "normal" when pin 8 is in circuit and "fast mode" when pin 9 is in circuit.

You must now cut the trace line leaving IC3 at pin 8 on the bottom side of the printed circuit board. BE CAREFUL! This modifies the clock line for 2MHz operation.
 
 

           *********************************************************
           *                                                       *
               ------------------------------------------------    *
              |         ----------  ----------  -----------    |   *
              |         |        |  |        |  |         |    |   *
              |         ----------  ----------  -----------    |   *
              |                      o---------------common------------switch
              |                  ------------------ ------     |   *     | |
              |                  |                | |    |     |   *     | |
              |                  ------------------ ------     |   *     | |
              |         --------           ---------           |   *     | |
              |         |      |     X     |       |           |   *     | |
              |         --------    R16    ---------           |   *     | |
              |                                                |   *     | |
              |         ------- ------- ------      ----       |   *     | |
              |         |     | |     | |    |      |  |       |   *    A| |B
              |         ------- ------- ------      ----       |   *     | |
              |                 !!=======================================|-|
           *   ------------------------------------------------    *
           *                    pins 8&9                           *
           *********************************************************

                                SSC pack