IA2910A Datasheet, PDF (4/19 Pages) InnovASIC, Inc – Microprogram Controller

IA2910A
Microprogram Controller
Page 4 of 19
Preliminary Data Sheet
pointer remains at zero whenever a POP is attempted from a stack already empty.
The register/counter is operated during three microinstructions (8, 9, and 15) as a 12-bit down
counter, with result = zero available as a microinstruction branch test criterion. This provides
efficient iteration of microinstructions. The register/counter is arranged such that if it is preloaded
with a number N and then used as a loop termination counter, the sequence will be executed
exactly N + 1 times. During instruction 15, a three-way branch under combined control of the
loop counter and the condition code is available.
The device provides three-state YOUT outputs. These can be particularly useful in designs
requiring automatic checkout of the processor. The microprogram controller outputs can be
forced into the high-impedance state, and pre-programmed sequences of microinstructions can be
executed via external access to the address lines.
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