smbakeryt has written an article on reverse-engineering the protocol used by the HP 27201A:
The HP 27201A is a TMS5220 based speech synthesizer released in 1983. According to the HP museum, it’s the first synthesizer designed by a major computer computer. Yes, the TI99/4A’s speech synthesizer uses the same IC and is at least contemporary if not even predating the HP module. The module has very sparse documentation on the web, so I had to disassemble the Z8 ROM and then reverse engineer the protocol.
See the full post on Scott M. Baker’s blog.
Check out the video after the break.