Data General ECLIPSE ®
Data Movement Instructions

    This page describes the instructions on the Eclipse that move data from one place to another. This includes memory- to- memory and memory- to- AC and vice- versa. Other pages describe:

• Architecture Overview
• NOVA Program Load Example
  • Fixed-Point Arithmetic Instructions
  • Floating-Point Arithmetic Instructions
  • Input/Output Instructions

    Since the Data General Eclipse operates primarily as a load/store machine it's fairly easy to lunp all the data movement instructions into a single basic class, which is what I've done here. The instructions listed here are the only ones which manipulate main memory directly, and most do so using a fairly simple addressing scheme. The way the Eclipse addresses memory was covered in detail in the Introduction to the machine.

    The basic memory- to- AC (and vice- versa) instructions in this class have a common format:

                         I          /---------- Displacement ----------\
                       /   \       /                                    \
   +---+---+---+---+---+---+---+---+---+---+----+----+----+----+----+----+
   | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 |
   +---+---+---+---+---+---+---+---+---+---+----+----+----+----+----+----+
   \                  /    \       /
    \--- Function ---/       Index  

    In general, instructions will be presented by their assembler mnemonics, followed by a short discussion of the instruction's function.

Load/Store Instructions

Load Accumulator (LDA)

              Accumulator    Index
               /       \   /       \
   +---+---+---+---+---+---+---+---+---+---+----+----+----+----+----+----+
   | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 |
   +---+---+---+---+---+---+---+---+---+---+----+----+----+----+----+----+
   \           /       \   /       \                                     /
    \  0 0 1  /          I          \---------- Displacement -----------/

Function:

The LDA instruction takes the data from the memory location addressed by "E", the effective address, and places it into the AC specified by bits 3 and 4. The previous contents of the AC are lost; the memory location and carry bit remain unchanged.

Assembler Syntax:

LDA AC, [@]D[, I]

Store Accumulator (STA)

              Accumulator    Index
               /       \   /       \
   +---+---+---+---+---+---+---+---+---+---+----+----+----+----+----+----+
   | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 |
   +---+---+---+---+---+---+---+---+---+---+----+----+----+----+----+----+
   \           /       \   /       \                                     /
    \  0 1 0  /          I          \---------- Displacement -----------/

Function:

The STA instruction stores the contents of the AC specified by bits 3 and 4 into the location specified by "E", the effective address. The previous contents of "E" are lost; the AC and carry are unaffected.

Assembler Syntax:

STA AC, [@]D[, I]

Increment/Decrement Memory Instructions

Increment and Skip if Zero (ISZ)

                         I          /---------- Displacement ----------\
                       /   \       /                                    \
   +---+---+---+---+---+---+---+---+---+---+----+----+----+----+----+----+
   | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 |
   +---+---+---+---+---+---+---+---+---+---+----+----+----+----+----+----+
   \                  /    \       /
    \    0 0 0 1 0   /       Index  

Function:

The ISZ instruction increments the contents of the location addressed by "E" by one and skips the next instruction if the result equals zero. The carry bit is unaffected.

Assembler Syntax:

ISZ [@]D[, I]

Decrement and Skip if Zero (DSZ)

                         I          /---------- Displacement ----------\
                       /   \       /                                    \
   +---+---+---+---+---+---+---+---+---+---+----+----+----+----+----+----+
   | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 |
   +---+---+---+---+---+---+---+---+---+---+----+----+----+----+----+----+
   \                  /    \       /
    \    0 0 0 1 1   /       Index  

Function:

The DSZ instruction decrements the contents of the location addressed by "E" by one and skips the next instruction if the result equals zero. The carry bit is unaffected.

Assembler Syntax:

DSZ [@]D[, I]

    This page described the Load/Store instructions of the Data General Nova minicomputer. Other pages describe:

• Architecture Overview
• NOVA Program Load Example

• Arithmetic/Logic Instructions
• Input/Output Instructions

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