User programable roms seem to have come out around 1972 as well as most MSI needed for a 4 bit data path.
The 20 bit cpu,looks to be the best design using the memory at the time: 1.5 us core. Floating point is 9 digits binary
with +- 76 exponent. Spring 1973 looks resonable for the ball park FPGA emulation. Concept design is like this PDP11.
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45_pdp_11_45.jpg [ 1.04 MiB | Viewed 4160 times ]
The 24 bit cpu,may be the best value for the money,as you get a 48 bit floating point number.(11 digits).Note sure if it
will fit in same case as the PDP 11-45.
Memory is still is the biggest cost of the machine.Floating point routines are slowly getting developed, as I have just the I/o to write.
The cross assembler needs to have floating point input routines written.
Ben.