Ok, we finally have a decap of the TMC027x/TMS027x/CD270x die:http://siliconpr0n.org/map/ti/cd2708n2l/top_metal_mit20x/
This is the die from the Speak and Math (French/Canadian version), CD2708N2L.
Note that the Speak and Math (USA) version uses an MCU labeled CD2704 so there probably is some as-of-yet unknown code change between this die and the USA one.
Comparing it to Sean Riddle's decap of the TMC0260 from the TI 5025 (see http://www.seanriddle.com/ti5025fulldie.jpg
), this die is definitely based on the tmc0260, but with more ROM, more RAM, and everything moved a bit farther apart from each other to make space for the extra routing lines etc. The segment PLA is larger with 48 terms instead of 32.
It uses 9-bit ROM words like the TMS0980.
The Segment PLA of the CD2708 probably does not match the speak and spell Segment PLA as it should have a few more math related characters in it.
The pinout of the CD2708 should match or nearly match the TMS0270 pinout, there may be a minor difference to allow driving a 9th digit of the VFD.
NOTE: the pinout chart of the TMS0270 I made was created before this decap was done and is likely to have errors and omissions! Do not hesitate to make corrections and/or stick the diagram in the MESS source code somewhere.
There is a patent on the Speak and Math which includes a code listing which should match (probably) the CD2704 USA version, US Patent 4,970,659 http://www.google.com/patents/US4970659.
The source code is in the text area as a TABLE so it doesn't show up in images in Google patents, so best is to use pat2pdf.org instead http://www.pat2pdf.org/patents/pat4970659.pdf
As far as I know, the Speak and Math code has never been typed up like the Speak and Spell patent code has been.
There are two different sets of two VSM(TMS6100 or TMS6125) speech ROMs for the Speak and Math:
CD2392 and CD2393 are two 16KiB VSM ROMs used on the apparently older speak and math units.
CD2381 and CD2614 are a 16KiB and a 4KiB VSM ROM respectively used on the apparently newer speak and math units, despite the first VSM being a lower number than the other two from the 'apparently older' units. (There's probably a story here...)