240 Part 3 The instruction-set processor level: variations in the processor
Section 4 Desk calculator computers: keyboard processors with small memories
record program switch is on, the keys specify the instruction to be recorded in the program memory. Finally, the descriptions specify the instruction's behavior as it is executed within a program.
Start S. The instruction S (used in creating a program) directs the computer to stop and release the keyboard for the entry of figures or the selection of a subroutine. After figure entry, the program is restarted by touching the start key (S).
The program can also be restarted by touching a routine selection key. When the S instruction stops the program, the computer may also be operated in the manual mode without disturbing the program instructions in the memory. Any figures entered on the keyboard before depression of start or an operation key will be printed automatically.
Clear *. The clear operation * directs the computer to clear the selected register. The M and R registers cannot be cleared with this instruction.
When the computer is operated manually this key will cause it to print the contents of the selected register, r. (r ¬ 0)
Data-transfer operations
To A ¯ . An instruction containing the operation ¯ directs the computer to transfer contents of the addressed register, r, to A while retaining them in the original register. The contents of M and R are not affected. The previous contents of A are destroyed. (A ¬ r)
From M . An instruction containing the operation directs the computer to transfer the contents of M to the addressed register while retaining them in M. The contents of registers A and R are unaffected by this instruction. The original contents of the addressed register are destroyed. (r ¬ M)
Exchange ½ . An instruction containing the operation ½ directs the computer to exchange the contents of the A register with the contents of the addressed register. The contents of M are not affected except by the exchange between A and M. The contents of the R register are not affected. (A ¬ r; r ¬ A)
D-R exchange RS. The instruction RS directs the computer to exchange the contents of D (both D and d registers) with the contents of the R register. (D ¬ R; R ¬ D)
This instruction has a special use in multicard programs to store temporarily the contents of the D (d,D) register in R, when a new card has to be read to continue the program. During this temporary storage no instruction affecting the R register should be executed.
Decimal part to M /½ . The instruction / directs the computer to transfer the decimal portion of the contents of A to the M register while retaining the entire contents in A. The original contents of the M register are destroyed. The R register is not affected by this instruction. (M ¬ fraction_ part(A))
Arithmetic operations
All arithmetic operations are performed in the operating registers M, A, and R. An arithmetic operation is performed in two phases:
1 The contents of the selected register are automatically transferred to the M register. The M register is selected automatically if no other register is indicated.
2 The operation is carried out in the M, A, and R registers.
Programma 101 can perform these arithmetic operations: +, - , x, ¸ , Ö , and absolute value. Figures are accepted and computed algebraically. A negative value is entered by depressing the negative key at any time during the entry of a figure. If there is no negative indication, the computer will accept the figure as positive.
The subtract operation key is separate from the numeric keyboard and is used exclusively for subtraction (not negation).
Addition +. An instruction containing the operation + directs the computer to add the contents of the selected register (addend) to the contents of the A register (augend). Addition is executed in two phases:
1 Transfer the contents of the selected register (addend) to M.
2 Add the contents of M to the contents of A (augend) obtaining in A the sum truncated according to the setting of the decimal wheel. The complete sum is in R. M contains the addend. (M ¬ r; next R ¬ A + M; next A ¬ f(R,decimal_ wheel))
Multiplication X. An instruction containing the operation x directs the computer to multiply the contents of the selected register (multiplicand) by the contents of the A register (multiplier).
1 Transfer the contents of the addressed register to M.
2 Multiply the contents of M by the contents of A, obtaining in A the product truncated according to the setting of the decimal wheel. The complete product is in R. M contains the multiplicand. (M ¬ r; next R ¬ A x M; next A ¬ f(R, decimal_ wheel))