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  • 參數(shù)資料
    型號(hào): MAR2910CD
    廠商: Electronic Theatre Controls, Inc.
    英文描述: RADIATION HARD MICROPROGRAM CONTROLLER
    中文描述: 輻射硬微程序控制器
    文件頁(yè)數(shù): 8/16頁(yè)
    文件大小: 216K
    代理商: MAR2910CD
    MA2910
    8
    Instruction 12: Load Counter and Continue.
    This instruction simply enables the counter to be loaded
    with the value at its parallel inputs. These inputs are normally
    connected to the pipeline branch address field which (in the
    architecture being described here) serves to supply either a
    branch address or a counter value depending upon the
    microinstruction being executed.
    Altogether there are three ways of loading the counter: the
    explicit load by this instruction 12; the conditional load included
    as part of instruction 4; and use of
    RLD
    input along with any
    instructions.
    The use of
    RLD
    with any instruction overrides any counting
    or decrementation specified in the instruction, calling for a load
    instead. Its use provides additional microinstruction power, at
    the expense of one bit of microinstruction width
    Instruction 12 is exactly equivalent to the combination of
    instruction 14 and
    RLD
    LOW. Its purpose is to provide a simple
    capability to load the register/counter in those implementations
    which do not provide microprogrammed control for
    RLD
    .
    The example shows the TEST END-OF-LOOP
    microinstruction at address 56. If the test fails, the
    microprogram will branch to address 52. Address 52 is on the
    stack because a PUSH instruction had been executed at
    address 51. If the test is passed at instruction 56, the loop is
    terminated and the next sequential microinstruction at address
    57 is executed which also causes the stack to be POP’d; thus
    accomplishing the required stack maintenance.
    Instruction 14: CONTINUE.
    This simply causes the microprogram counter to increment
    so that the next sequential microinstruction is executed. This is
    the simplest microinstruction of all and should be the default
    instruction which the firmware requests whenever there is
    nothing better to do.
    Instruction 15: Three-Way-Branch.
    This instruction is the most complex and provides for
    testing of both a data-dependent condition and the counter
    during one microinstruction and provides for selecting among
    one of three microinstruction addresses as the next
    microinstruction to be performed. Like instruction 8, a previous
    instruction will have loaded a count into the register/counter
    while pushing a microbranch address onto the stack.
    Instruction 15 performs a decrement-and-branch-until-zero
    function similar to instruction 8. The next address is taken from
    the top of the stack until the count reaches zero. When the
    counter reaches zero the next address comes from the
    pipeline register. The above action continues as long as the
    test condition fails. If at any execution of instruction 15 the test
    condition is passed, no branch is taken and the microprogram
    counter register furnishes the next address. When the loop is
    ended, either by a count becoming zero, or by passing the
    conditional test, the stack is POP’d by decrementing the stack
    pointer, since interest in the value contained at the top of the
    stack is then complete.
    The application of instruction 15 can enhance
    performance of a variety of machine-level instructions. For
    instance: (1) a memory search instruction to be terminated
    either by finding a desired memory content or by reaching the
    search limit; (2) variable-field-length arithmetic terminated
    early upon finding that the content of the portion of the field still
    unprocessed is all zeroes; (3) key search in a disc controller
    processing variable length records; (4) normalization of a
    floating point number.
    Figure 15: 12 LD CNTR & CONTINUE (LDCT)
    Instruction 13: Test End-of-Loop.
    This instruction provides the capability of conditionally
    exiting a loop at the bottom; that is, this is a conditional
    instruction that will cause the microprogram to loop via the file
    if the test is failed, else to continue to the next sequential
    instruction.
    Figure 16: 13 TEST END LOOP (LOOP)
    Figure 17: 14 CONTINUE (CONT)
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