I had a quick look at the software yesterday comparing Black Knight to Jungle Lord.
Jungle Lord raises the speech clock line (6821 CB2) high, then clears it two instructions later.
Black Knight uses features of the 6821 to synchronise the CB2 speech clock pulse against the "E" clock from the CPU and a port B write. This method looks like the clock signal is opposite phase compared to Jungle Lord.
A cursory look at the generation of the speech data signal was also different.
Suffice to say they are rather different from a software perspective.

Yes. And before you ask, I replicated the Jungle Lord clock code into Black Knight but it didn't work off the bat under emulation (voice went missing). Other code around it is not the same.

Just a reminder, barakandl said the problem also occurs on original boards with a 55564. It's not specific to his new board.

Sys7_Speech.png

The first two Black Knight instruction descriptions I posted above explain how the 6821 CB2 signal is pulsed for the CVSD clock signal (taken from the 6821 datasheet). The pulse ultimately takes a period of one CPU E clock. A 3.58MHz crystal is hooked up to the 6802 CPU which internally divides it by 4 resulting in the E clock signal having a period of about 1.1us. That's the time length of the CB2 low going pulse to clock the CVSD in the Black Knight waveform shown above.
This is an unforeseen implementation issue for the 55536/55564 but like you said, poor Harris datasheets probably didn't help.

barakandl now has working software fixes based on manually changing the PIA CB2 state like Jungle Lord. Interestingly, Gorgar which was the first Williams game with speech is what Jungle Lord CVSD code was based on. So they did it correctly to start with.
Black Knight and Alien Poker were likely done by a different programmer to the other speech games as these two also implemented the ability to change voice pitch, both of which have the issue with 55536/55564.

The challenges are that Black Knight has no free ROM space, and the instruction cycle count needed to be maintained in order to keep the voice pitch the same since the software loop for spitting out the data stream to the CVSD is CPU execution timed. But it was managed.

Another minor software error they made was at the very start of any spoken word, the clock signal is pulsed *before* the first valid speech bit is applied to the CVSD data input.

Yes. Both implementations update the clock and if all data bits are processed then exit, otherwise apply a data bit and loop back to the clock update. This is slightly simplified but there is one extra CVSD clock pulse at the very beginning of every word stream. All speech is broken up into single words so they could create multiple phrases by grouping different words.

See below - the extra first CVSD clock will have a different effect because of the different clock phase between say Black Knight and Jungle Lord. Of course the error is not perceivable being only a single output bit step.

The 55564 data sheet says the data bit is strobed in on the rising edge of the clock. On the falling edge of the clock, the 55564 output is updated.

Heh, only two years before there were still games with mechanical chimes/3 simple electronic tones being manufactured. Things were changing fast.

We wish!