If numbering in hh_tms1k holds then MP1296 should be a tms1100; if the chip is rev E or later it cannot be easily dumped due to the addition of what we assume was a security feature on the die (which Kevtris calls the "Fuck-you-FET") which holds the d7 rom line permanently in one state during dumping/test mode, preventing that bit from being read out. Die revisions D and older of the tms1100 will dump fine (although we cannot read the MPLA (custom instructions) or OPLA (segment/output) data without a decap)
Do you have a picture of the chip itself including all markings?
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