The TMS9900 COU was the first 16-bit microprocessor that could effectively compete in the computer market. In fact the TMS9900 is a single chip implementation of the TM Seiries 990 minicomputer CPUs.
The 9900 has a seperate 16 bit address bus and a 16 bit data bus in a 64 pin DIP.
The 9980 has an 8 bit data bus and 14 bit addressbus but is otherwise the same.
The 9940 is a one-chip solution with onboard memory and real-time clock circuit.