## EDSAC Rebuild Project - Logic Reconstruction - Clock

 Accumulator Shifting Unit 1 Accumulator Shifting Unit 2 Accumulator Main Adder Computer Control I Computer Control X Computer Control II Computer Control III Computer Control IV Computer Control V Computer Control VI Computer Control VII Computer Control VIII Computer Control IX Coincidence Unit Clock Generator Complementer/Collater Control Switches and Logic Counter Digit Pulse Generators Engineers Control Panel Frigs Half Adder Type 1 Half Adder Type 2 Main Control Unit Multiplicand Tank Memory Units Multiplier Tank Order Coder Order Decoder 1 Order Decoder 2 Order Flashing Unit Order Tank Printer Sequence Control Tank Clock Generator This is the Clock generation unit. This generates the basic timing pulses for use in the rest of the logic. The elements at left are simulated pulse generators. The one nearest the top generates a continuous stream of pulses at 2.0 μsec intervals. Each pulse is 0.9 μsec wide. The other two generate one pulse every minor cycle (36 clock pulses). In the original machine the clock oscillator was divided by 36 and the output was designated D17. The remaining pulses were generated by delaying the previous pulse by 1 or 2 pulse intervals. This caused me some problems in my simulation, and so I have inserted a pulse element to generate D0, so that my simulation starts with a D0 pulse. Simply ignore this and connect the delay 'dl0' to the output D0. The clock does not appear on the original logic drawings, but the two main elements - the clock pulse generator and the delay elements appear in two circuit diagrams which were found in the Archives. The circuit for the delay elements specifies components for a 2 μsec delay, but it also says that there are twenty of these, in 5 panels of 4 stages per panel. As not all the digit pulses are required, it was found that making some of the delays equal to two pulse intervals (4 μsec) that it was possible to produce all the required pulses with twenty stages. In order to do this we had to start from D17, which explains why this was chosen as the starting pulse.