Re: CVSD

Yeah, I saw that info on Larry Bank's web page. Im waiting to hear
back from him now actually. If I find a data sheet I will forward it
to you to archive on spies.
 thanks
   jess

Al Kossow wrote:
>
> here are a few pointers. FWIW, the Exidy gun games have four of the MC3417's on
> them..
>
> How I got speech to work in Sinistar
>
> Several people have asked me how I got sinistar to speak. Instead of responding to each one individually, I figured it would be easier to
> post the code here. First, I want to thank Sean Riddle for helping me find the information I needed to simulate the operation of the speech
> compression chip. Sinistar has a Harris 55564 CVSD (Continuously Variable Slope Delta-Modulator) which uses a 1bit stream of data to
> simulate the ups and downs of an audio signal. The Harris data sheet doesn't say a whole lot, so I found a similar chip from Motorola
> (AN1544) which had a decently detailed data sheet. Like the DAC used to generate digitized sounds, the 55564 is hooked up to the PIA on
> the 6808 through two 1-bit ports (1 for clock, 1 for data). I examined the operation of the 6808 code and it places the data on the output bit
> when it changes, and toggles the clock bit at a rate of 16Khz. The basic way that it works is that the 1 bit data stream adds or subtracts the
> delta value from the current 10-bit DAC counter. A flat (silent) analog signal would produce a series of alternating ones and zeros. There
> is a 3-bit shift register which detects over or underflow conditions (when the step value is too small to keep up with the slope of the signal).
> When this condition occurs, the step value is incremented, otherwise it is decremented. So...the step value is constantly changing to meet
> the conditions of the compressed data. The step value changes based on an RC network which has a time constant of 4ms. I do not have
> good details about how the step value is chosen, but my approximation at least gives speech that you can understand. My Sinistar
> emulation still does not play perfectly because I am not simulating the operation of the 6821 properly and this game makes heavy use of
> proper 6821 behavior. This will have to be left for a future date...
Received on Fri May 21 16:27:00 1999