EMMA 02

System 00

Operating Procedures

The procedures below follow Section III of the 1971 System 00 manual and work unchanged on the emulated front panel. The switch and LED names refer to the controls described in the Front Panel section.

Power on

After power on, press SP and CL. The SP and ID LEDs are both on: the clock is stopped and the CPU is in the idle state. The system is now ready for one of the procedures below.

Initial program load

This procedure loads a program into memory from the hex keypad, starting at address 0000 (hexadecimal):

  1. Set the LOAD switch off.
  2. Press CL.
  3. Press ST.
  4. Set the LOAD switch on. The NB LED turns on, ready for the first byte.
  5. Enter each byte with two key presses: the least significant digit first, followed by the most significant digit. The byte is stored when the second digit is entered, the bit LEDs display it, and the NB LED turns on again for the next byte. Bytes are stored sequentially.
  6. When loading is complete, set the LOAD switch off and press SP.

Note: The punched card reader of the original System 00 is not emulated; programs are entered with the hex keypad or loaded from the host computer.

Load memory address check

To verify how many bytes were loaded and where loading ended, press SP and set the MN switch on after loading. With the Bus Select switches set to 100, the bit LEDs show the high byte of the address one past the last byte stored; with 010, they show the low byte.

Program initiation

  1. Set all toggle switches off.
  2. Press CL.
  3. Press ST. The clock runs and the CPU sits in the idle state.
  4. Press RS. The idle instruction is terminated and the CPU fetches and executes the instruction at the next address.

Note: After CL the CPU idles at address 0, so execution starts at address 1.

To stop the program, press SP; the clock stops cleanly at the end of the current machine cycle. Press ST to resume without error.

Reading memory

  1. Press SP.
  2. Press CL.
  3. Press ST.
  4. Set the READ switch on. The bit LEDs display the memory byte at the current address.
  5. Press RS to step to the next address; the bit LEDs display the next byte.
  6. Set the READ switch off when finished.

Setting registers

  1. Press SP, press CL, and set the MN switch on.
  2. Set the R Select switches to the number of the register (0 to F).
  3. Set the R1 and R0 switches to select the byte or bytes to write.
  4. Set the 0-7 switches to the desired byte.
  5. Press WR. The byte is written into the selected register, and the register is copied into the address register.
  6. Set the Bus Select switches to 100 and 010 in turn to display the high and low bytes of the register just set.

Setting memory bytes

  1. Press SP, press CL, and set the MN switch on.
  2. Set R(0) to the target address with the register setting procedure above (R Select set to 0). The address register now holds the target address.
  3. Set the 0-7 switches to the desired byte.
  4. Press WM. The byte is stored at the target address.
  5. Set the Bus Select switches to 001 to display the byte just stored.

Clearing memory

  1. Press SP, press CL, and set the MN switch on.
  2. Set the 0-7 switch labelled 6 on; the bit LEDs show 01000000.
  3. Press WIN. This writes 4 into the I register and 0 into X.
  4. Set the MN switch off and the RPT switch on.
  5. Press ST. The CPU repeatedly executes the instruction, stepping through all memory locations in read mode.
  6. Briefly set the CM switch on. All memory locations are cleared to 0.
  7. Set the RPT switch off.

Stepping through a program

Set the MC switch on to execute exactly one machine cycle each time ST is pressed. Set the RPT switch on to repeat the current machine cycle continuously; with both switches on, each ST press executes one repetition. Set MC and RPT off and press ST to resume normal execution.