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378 Part 4 The instruction-set processor level: special-function processors

Section 4 Processors based on a programming language

Fig. 5. Arithmetic statement loading.

or it puts the data address into the program. The 8-bit BCD forms of the operator symbols are simply put into the program. The constants are put into the program after conversion to machine form. The state diagram of this circuit is shown in Fig. 5. The scan circuit signal ARITH STAT sends the circuit from 0 through 1 to 2. The scan circuit has saved the address of the beginning of this statement in a register SCIO. This is used to initialize the CIO so that this statement can be read from the beginning.

The first symbol of an arithmetic statement, which must be a variable and not a digit, takes the circuit to state 3 after this symbol has been put into the program (Sv ® PROG) and the VMU initialized and started. Any one of the VMU signals is possible and valid and simply forces the circuit to state 5. During the 3-5 transition the circuit loads the appropriate address into the program when the name has matched. If it has not matched any existing name the circuit first goes to state 4 and puts the name into the Symbol Table before going to state 5. State 5 is that from which all further loading is accomplished. Variable names are separated by operators, which are loaded into the program by the cycle in state 5 (S0 ® PROG). Note the convention that S0 represents any operator symbol not explicitly specified on another exit from 5. Any variable names cause a transition to state 3 with the same output action as from state 2. Floating point constants are loaded via states 5-9-5. A decimal point indicates a floating point constant and takes the circuit to state 7. (Note that a minus sign preceding a constant is simply an operator and is processed in state 5.) The SHR is cleared in preparation for the storing of the following digits in state 7. When E is received 'the digits of the fraction in the SHR are left adjusted (ADJUST SHR), if there are less than four of them, and placed in the program area. The exponent sign is found in the transition 8 to 9. The exponent digit together with the exponent sign bit is stored in the program area during the

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