tms 9900

1 definition found

tms 9900 - Free On-line Dictionary of Computing (26 May 2007) :

  TMS 9900
  
     <processor> One of the first true 16-bit microprocessors,
     released by Texas Instruments in June 1976 (the first are
     probably National Semiconductor IMP-16 or AMD-2901 bit slice processors
      in 16-bit configuration).  It was designed
     as a single chip version of the TI 990 minicomputer
     series, much like the Intersil 6100 was a single chip
     PDP-8, and the Fairchild 9440 and Data General mN601
     were both one chip versions of Data General's Nova.
     Unlike the IMS 6100, however, the TMS 9900 had a mature, well
     thought out design.
  
     It had a 15-bit address space and two internal 16 bit
     registers.  One unique feature was that all user registers
     were actually kept in memory - this included stack pointers
     and the program counter.  A single workspace register
     pointed to the 16 register set in RAM, so when a
     subroutine was entered or an interrupt was processed, only
     the single workspace register had to be changed - unlike some
     CPUs which required dozens or more register saves before
     acknowledging a context switch.
  
     This was feasible at the time because RAM was often faster
     than the CPUs.  A few modern designs, such as the INMOS
     transputer, use this same design using caches or rotating buffers
     , for the same reason of faster context switches.
     Other chips of the time, such as the 650x series had a
     similar philosophy, using index registers, but the TMS 9900
     went the farthest in this direction.
  
     That wasn't the only positive feature of the chip.  It had
     good interrupt handling features and very good instruction
     set.  Serial I/O was available through address lines.  In
     typical comparisons with the Intel 8086, the TMS9900 had
     smaller and faster programs.  The only disadvantage was the
     small address space and need for fast RAM.
  
     Despite very poor support from Texas Instruments, the TMS 9900
     had the potential at one point to surpass the Intel 8086 in
     popularity.
  
     (1994-11-30)