devorn

Yes, thank you for the encouragement and info , ... and the TI hardware seems to have such a great Fourth implementations and community. I'll definitely be discussing with you further once I have my RAM sorted out. ... I am also thinking that perhaps I will pick up a TI-99 at some stage to complement the /189 (it's older cousin). Thanks all for the kind words and feedback. I will let the thread get back to it's primary Geneve 2020 debugging mission now.

@FarmerPotato : Thank you, I will check these out in the next few days...

Well, yes, ... there is a space for additional EPROM/ROM on the board and that is actually a longer term goal. ... But first, a memory expansion board (off-board RAM) to be homebrewed using static RAM and some address decoding logic. This board is a TM990/189 and not so fully featured out of the box. According to the well documented users guide/manual (Jan 1979) from TI, off-board memory expansion is factored into the original design and should be possible via the expansion connectors provided ... I can see no evidence on the internet that anyone has actually done this yet for this particular model board ... (undoubtedly it has been done before but pre-internet age). ... It will be a learning experience and I still have plenty to learn along the way. As for software, it will need to be cross assembled on another machine (x86 ?) for now, as I have no other TI machines apart from the TM990/189.

@FarmerPotato thanks for the comments and suggestions on how to obtain more reliable TMS9902A's Well, I took the plunge and equipped my vintage board with a NOS Winchester Electronics DB25S connector, three resistors, a TI 75188 from a known good source, and a TMS9902NL as described in my previous post. First power up, the machine did not like it at all and continuous Beeps (BEL) were emitted as soon as I attempted to initialise the RS232 port. Suspecting the TMS9902, I tried a second (..., after all I purchased 10 at a very reasonable price). .... it quietened down immediately and all seemed OK. Connected to a PC via the serial port (a proper RS-232 tolerant one, no USB-> serial adapters),... and was conversational using Hyperterm and Teraterm straight away. No sync errors even after 2 hours, seems to work perfectly fine so far. As suspected, I guess that the TMS9902NL chips were indeed genuine (albeit blacktopped and remarked) and at least some of the batch work well.

mmm, with regard to the TMS9901NL's from Po**da, I have also received a number of the DBS 8815 marked chips (10). I is somewhat doubtful that TI was still manufacturing the original TMS9901NL in 1988..? Careful inspection shows: - Clean black tops with labelling that is questonable in regard to authenticity (refer stargunner's posts) - Injection mold marks etc. seem to be as they should be - Underneath of chips vary, and some indicate some stress from being subjected to heat/desoldering, general usage in equipment etc. In contrast to the tops - Legs are shiny, dipped in solder - small nicks and defects in some when examined under a magnifying glass, but covered in shiny solder; - Pin orientation straightened to resemble manufacturers spec sheet or close; - Like stargunner mentioned, some light printing on the underside, mostly all rubbed off. - Two chips still legible with printing 'D9902S/17251 SINGAPORE' and 'D9902S/1**47 SINGAPORE' (? 2nd one difficult to read). Does not look like it is printed to stay on long term. My theory is that at least some of these may be real chips (or even some completely different chip in some cases?) that have been recovered from e-waste via various desoldering techniques. sorted and temporarily stamped on underneath with identifying chip, legs straightened, dipped in solder... Later (quite some time later) assembled into a large batch, tops cleaned and oversprayed with new identification 'DBS8815 PHILIPPINES'.. distributed for sale. The 'S' in the underside suffix of 'S' may also give us some clues? ... D9902S American Microsystems Inc. was a alternative source supplier of TMS9902 ACC compatible chips. Theirs was called an S9902 in their Winter 1979 product catalog. https://usermanual.wiki/Document/1979AMIMOSProducts.1693266659.pdf ( 5.44 (p326) ) I am yet to discover whether any or all of them work per spec (will report in a few weeks or over Xmas holidays). It is possible that some work, others may not. Has anyone verified whether their batch of purported TMS9902 'DBS 8815' actually function per spec?

This one is quite early. The disk seems to be of DOS 3.2 era 13 sector type....so it would only boot in an Apple II with the original Disk ][ controller fitted with the 13 sector type PROMS,.. or one would need to use BOOT13 from the DOS 3.3 Master disk when used with a more modern Disk ][ controller + drive.