Table of Contents for Programming Languages: a survey

Minimalistic and pedagogical Assembly Language ISAs

LMC (Little Man Computer)

pedagogical

http://teaching.idallen.com/dat2343/10f/notes/301_LMC.html

https://en.wikipedia.org/wiki/Little_man_computer

" Instructions Numeric code Mnemonic code Instruction Description 1xx ADD ADD Add the value stored in mailbox xx to whatever value is currently on the accumulator (calculator).

    Note: the contents of the mailbox are not changed, and the actions of the accumulator (calculator) are not defined for add instructions that cause sums larger than 3 digits.

2xx SUB SUBTRACT Subtract the value stored in mailbox xx from whatever value is currently on the accumulator (calculator).

    Note: the contents of the mailbox are not changed, and the actions of the accumulator are not defined for subtract instructions that cause negative results - however, a negative flag will be set so that 8xx (BRP) can be used properly.

3xx STA STORE Store the contents of the accumulator in mailbox xx (destructive).

    Note: the contents of the accumulator (calculator) are not changed (non-destructive), but contents of mailbox are replaced regardless of what was in there (destructive)

5xx LDA LOAD Load the value from mailbox xx (non-destructive) and enter it in the accumulator (destructive). 6xx BRA BRANCH (unconditional) Set the program counter to the given address (value xx). That is, value xx will be the next instruction executed. 7xx BRZ BRANCH IF ZERO (conditional) If the accumulator (calculator) contains the value 000, set the program counter to the value xx. Otherwise, do nothing.

    Note: since the program is stored in memory, data and program instructions all have the same address/location format.

8xx BRP BRANCH IF POSITIVE (conditional) If the accumulator (calculator) is 0 or positive, set the program counter to the value xx. Otherwise, do nothing.

    Note: since the program is stored in memory, data and program instructions all have the same address/location format.

901 INP INPUT Go to the INBOX, fetch the value from the user, and put it in the accumulator (calculator)

    Note: this will overwrite whatever value was in the accumulator (destructive)

902 OUT OUTPUT Copy the value from the accumulator (calculator) to the OUTBOX.

    Note: the contents of the accumulator are not changed (non-destructive).

000 HLT/COB HALT/COFFEE BREAK Stop working. DAT DATA This is an assembler instruction which simply loads the value into the next available mailbox. DAT can also be used in conjunction with labels to declare variables. For example, DAT 984 will store the value 984 into a mailbox. "

CARDIAC

" CARDIAC had a 10 instruction machine language. An instruction consisted of three decimal digits (the sign is ignored). The first digit was the op code (O), the second and third digits comprised an address (A). Addressing was one of accumulator to memory absolute, absolute memory to accumulator, input to absolute memory and absolute memory to output.

    OAA

High level languages were never developed for CARDIAC, since they would defeat one of the purposes of the device, to introduce concepts of assembly language programming.

Programs were hand assembled, then written, by pencil into the appropriate memory cells. Instruction Set CARDIAC Instruction Set Opcode Mnemonic Instruction Description 0 INP Input take a number from the input card and put it in a specified memory cell. 1 CLA Clear and add clear the accumulator and add the contents of a memory cell to the accumulator. 2 ADD Add add the contents of a memory cell to the accumulator. 3 TAC Test accumulator contents performs a sign test on the contents of the accumulator; if minus, jump to a specified memory cell. 4 SFT Shift shifts the accumulator x places left, then y places right, where x is the upper address digit and y is the lower. 5 OUT Output take a number from the specified memory cell and write it on the output card. 6 STO Store copy the contents of the accumulator into a specified memory cell. 7 SUB Subtract subtract the contents of a specified memory cell from the accumulator. 8 JMP Jump jump to a specified memory cell. The current cell number is written in cell 99. This allows for one level of subroutines. 9 HRS Halt and reset move bug to the specified cell, then stop program execution. " -- [1]