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IA2910A

Microprogram Controller

Copyright

© 1999, InnovASIC Inc.

Customer Specific IC Solutions

either identical to the YOUT output, or else one greater, as determined by CIn. For each

instruction, one and only one of the three outputs PLn, MAPn, and VECTn is LOW. If these

outputs control three-state enables for the primary source of microprogram jumps (usually part of a

pipeline register), a PROM which maps the instruction to a microinstruction starting location, and

an optional third source (often a vector from a DMA or interrupt source), respectively, the three-

state sources can drive the DIN inputs without further logic.

Several inputs, as shown in Table 2, can modify instruction execution. The combination CCn

HIGH and CCENn LOW is used as a test in 9 of the 16 instructions. RLDn, when LOW, causes

the DIN input to be loaded into the register/counter, overriding any HOLD or DEC operation

specified in the instruction. OEn, normally LOW, may be forced HIGH to remove the IA2910A

YOUT outputs from a three-state bus.

The stack, a nine-word last-in, first-out 12-bit memory, has a pointer which addresses the value

presently on the top of the stack. Explicit control of the stack pointer occurs during instruction 0

(RESET), which makes the stack empty by resetting the SP to zero. After a RESET, and

whenever else the stack is empty, the contents of the top of stack is undefined until a PUSH occurs.

Any POPs performed while the stack is empty put undefined data on the F outputs and leave the

stack pointer at zero.

Any time the stack is full (nine more PUSHes than POPs have occurred since the stack was last

empty), the FULLn warning output occurs. This signal first appears on the microcycle after a ninth

PUSH. No additional PUSH should be attempted onto a full stack; if tried, information within the

stack will be overwritten and lost.