IBM 1410 FPGA Simulation – The Brainstem

Additional work has resulted in another step forward in my efforts to reproduce the IBM 1410 (in particular, the IBM 1411 CPU component) in an FPGA.

I now have pages 11.10.0*.1, 11.10.10*.1 and 11.10.20*.1 generated and tested (see the image, below).

One very hopeful sign is that easily 90% of the effort in the last couple of days was enhancing the application to preserve a section of VHDL declarations in a test bench, and debugging VHDL test bench code. The generated HDL had performed nearly flawlessly.

In the image below one case see the following (MS… signals are a translation of -S IBM signals – active low. PS are +S – active high.

  • The simulated 100 MHz FPGA clock
  • The 1.5 MC (MHz for you modern people) system oscillator
  • The two phase system clock pulses
  • A test bench provided MS_PROGRAM_RESET_3 signal, provided by the test bench.
  • The logic ring gates A through K and R through W. The latter are only active in the last part of the test, and represent an overlapped I/O request (cycle-stealing, if you prefer)
  • A test bench provided PS_LAST_LOGIC_GATE_1 signal – telling the logic gate ring that it can go back to the initial “A” state.
  • A non-overlapped I/O cycle request (E Cycle means a cycle taken for the first, or E channel – not to be confused with logic gate E)
  • An overlapped I/O cycle request on the first channel
  • The PS_COM_DISABLE_CYCLE which “freezes” the logic ring – overridden by the non-overlapped E cycle request.
IBM 1410 Logic Gate Ring Simulation
A Xilinx Vivado simulation of the IBM 1410 Logic Gate Ring

The FPGA Simulated IBM 1410 has a “pulse”

Having spent the past few months cleaning up my IBM 1410 SMS database program, and posting it to github at , I have spent the past couple of weeks focused on the HDL (currently VHDL) generation, using GHDL and Xilinx’s Vivado toolset, with an eventual destination of my Digilent Nexys4 FPGA (Field Programmable Gate Array) board.

After fixing a few bugs, and implementing the oscillator (by way of a counter/divider from the 100 MHz FPGA clock), I loaded the results into the FPGA, and as show below, my IBM 1410 now has a clock, running at the right frequency for an IBM 1410 with the accerated throughput feature, as shown below:

IBM 1410 FPGA Clock
IBM 1410 FPGA Clock

On the original machine the lower signal, on channel 2 of the oscilloscope, was derived from the first using a delay line – about 330 ns of delay. Kinda hard to do with an FPGA. 😉 So, I implemented delay lines using a series of flip flops clocked by the 100 MHz FPGA clock – so, in this case, there are 33 of them.

This signal is not simulated – it is a real signal that exists in the FPGA.