Subroutine calls may also be available at the microprogram level; however, the nesting level is typically restricted by the size of a dedicated control store return address stack.
For use in decoding macroinstructions, the initial mapping to a particular microprogram can be accomplished by one of these methods:
- appending low-order zeroes to the macroinstruction opcode, implying that the microcode routines are organized as fixed-offset segments within the control store (as in Wilkes’ original scheme)
- appending high-order zeroes to the macroinstruction opcode, implying the use of a jump table in low memory
- using a table lookup via a special decoding ROM or PLA (as in the 68000)
This initial mapping produces a control store address for the first microinstruction in a microprogram, and the microprogram sequencing (or “flow”) continues until the microprogram is complete. This is shown in Figure below.
The Joint Admission and Matriculation Board (JAMB), established by Decree No 2 of
1978 (amended by Section 5 of Decree 33 of 1989) was Nigeria‟s official entrance examination
board for candidates seeking admission to the nation‟s universities. Before then, the nation‟s
existing universities conducted what they referred to as their „concessional‟ entrance
examinations for prospective students. The process of administering the examination, on the
part of the candidates, was not only time-wasting, but was untidy and uncoordinated, especially
with the increasing number of universities as well as prospective candidates.
Some of its functions are to generally control the matriculation examination for
admissions into all universities, polytechnics and colleges of education in Nigeria; to appoint
examiners, moderators, invigilators, members of the subject panels and committees and other
persons with respect to Matriculation Examinations and any other matters incidental thereto or
connected therewith and to place suitably qualified candidates in the tertiary institutions. The
Board also undertakes the conduct of the Universities Matriculation Examination (UME) and
sends the results to universities chosen by the candidates, so that each university selects and