The Index Adder is a 15 bit ring accumulator. The sum of an instruction
base address, Y, and the contents of an index register, C(x), are formed
in this register. This register holds the previous content of the
Program Counter in the "jump and save Program Counter," jps,
instruction. The Index Adder also serves as the step counter in shift,
multiply, and divide.
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The Control Element contains two six bit registers and several
miscellaneous flip-flops. The latter deal with indexing, indirect
addressing, memory control, etc. The six bit registers are: