The first few seconds of the CFT's microcode sequencer running at the breakneck speed of 1 Hz. The sequencer, which takes up most of Processor Board 0 (PB0) has been manually configured to execute microcode for the TRAP instruction. It's front panel driver is connected to just one of the front panel modules, but it's enough to show some status. The top line of the FPM shows the value of the 4-bit microprogram counter. It goes up from 0000 until the end of the microprogram (when the leftmost LED on the second row turns off), at which point it resets back to zero. The second row shows some of the control signals including END (leftmost), R (second) and INCPC (first from the right). These are all active-low signals, so the lights turn off when signals are asserted. The third line is the RUNIT field: it identifies which processor unit drives the bus. The fourth line is the WUNIT field, which identifies what unit gets its value from the bus. The instruction being run is instruction 0, TRAP: Step 0000 (0): instruction fetch, phase 0. Set the Address Register with the value of the Program Counter. Step 0001 (1): instruction fetch, phase 1. Read from memory. Set the Instruction Register to the value of the Data Bus. Increment the Program Counter. The instruction fetched is TRAP again (because it's hardwired with, er, wires). Step 0010 (2): execute. Set AR to constant value 1. Step 0011 (3): write PC to memory address AR (1). Step 0100 (4): Set PC to memory address specified in the operand field of the instruction. End of microprogram.

• published: 01 Sep 2013
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