Chapter 11 The Pilot ACE 197

DL1₂ will have passed into the special TS marked TS COUNT during minor cycle number 2. By the end of minor cycle number 3, S switch number 16 will be over and also N switch number 2. The contents of TS16 will be passing into HIGHWAY and those of DL2 into INSTRUCTION HIGHWAY. At the beginning of minor cycle number 12 (i.e. 2 + 8 + 2), D switch number 20 will go over, and TS20 will stop recirculating and the number on the HIGHWAY will pass into TS20. The transfer will continue until minor cycle 14 (i.e. 2 + 10 + 2) when the D switch number 20 will switch back. At the beginning of minor cycle 14, the switch X on COUNT will go over and the number on INSTRUCTION HIGHWAY during this minor cycle, DL2₁₄, will pass into COUNT. At the end of minor cycle 14, the X switch will close again and DL2₁₄ will be trapped in COUNT. The cycle of events is now complete. COUNT is associated with a counter and it is this counter which determines from the wait, timing, and characteristic numbers of the trapped instruction, when the D and X switches go over and back.

The only part of the instruction word not described is the GO digit. If the GO digit is a one, the instruction is carried out at high speed, but if it is a zero the machine stops and does not proceed until a manual switch is operated. The GO digit is omitted in strategic instructions when a programme is being tested. It also