SIM4-02 HARDWARE SIMULATOR
1.0 INTRODUCTION
The SIM4-02 Hardware Simulator is a program written for the MCS-4 ™ series Micro Computer System. This program will provide interactive control over the debugging of other MCSA ™ programs.
The minimum configuration requited is a SI M4-02 prototype card with three 4002 RAMs and a Teletype. When fully stuffed with 16 RAMs, test programs up to 512 bytes (locations) in length may be accomodated. The hardware simulation program itself occupies nine full ROMs.
The Hardware Simulation Program has two basic functions:
1.To simulate the execution of a test program, tracing its progress, and apprehending gross errors.
2.To allow the user to dynamically interact with and/or modify his test program, in order to facilitate the debugging process.
These two functions are implemented by means of a set of directives or commands which the user types in at the teletype keyboard. Some of the directives call for typeouts by the simulator program, some of the directives signal the input of data or program modifications, and some of the directives involve both typeouts and input response or data.
A directive is identified by a single letter of the alphabet (except the arithmetic conversion directives = and It). If the directive is associated with output only, the typing (or punching) will commence immediately. If input is allowed or re- quired with the directive, the simulation program will enable the paper tape reader control, and wait for valid input data.
2.0 NUMBER SYSTEMS
Two number radices are standard with the hardware simulation program: binary and decimal. Index register values, pro- gram counter and instruction location values, chip numbers, and some pointers are handled in decimal for convenience. ROM instructions, the accumulator value, and one-bit indicators are handled in binary. Any input number may be entered in either radix by prefixing it with a suitable indentifier ("0" for decimal, "8" for binary), regardless of the expectations of the program. Unless so identified, however, all input should be in the radix used in the corresponding typeout.
To facilitate working with program tapes in the "BNPF" format, the hardware simulation program will accept binary num- bers coded either as strings of ones and zeroes, or as strings of "P"s and "N"s, where the letter P is interpreted as a zero, and the letter N is interpreted as a one.
All input numbers are right-justified into the receiving register or field. If the number is smaller than the receiving field, leading zeroes are implied as necessary. If the number is larger than the receiving field, the excess bits are lost from the most- significant end of the number. Thus, if it is attempted to load an index register with the value 20, the result will be 4 in the register. This may be used to advantage in the event of an inadvertant error typein, by typing in as many zeroes as there are bits in the receiving field, then re-typing the number, all as one string of digits. A number typed in may end with a carriage return, a comma, a space, or the letter "F", or in the case of the = directive, with plus or minus sign. Any other characters will give unpredictable results, and should be avoided. Rubouts are the only non "numeric" characters which may be imbed- ded within the input number strings with no adverse effects. Rubouts are ignored in all cases.
3.0 DESCRIPTION
The hardware simulation program allocates a user-selected block of RAM main memory locations to hold the ROM instruc- tions to be simulated, assigning two RAM locations for each simulated ROM location. Thus, to simulate 512 locations of ROM, all 16 RAMs must be used. Any RAM locations not allocated for program storage may be accessed in the normal way by the test program. In addition, the hardware simulation program uses the status characters in twelve consecutive RAM registers (equivalent to three RAM chips) to hold simulation parameters. RAM is assumed to be organized as four consecu- tive banks (with wraparound) of sixteen registers each, so that if less than 16 RAMs are used, those allocated to program and parameter storage must be in one block of contiguous banks and registers within banks.
The program to be tested may have an address anywhere in the 4096 locations of addressable, ROM, since the hardware simulator program adds a bias value to all addresses which reference the simulated ROM. If the program attempts to jump or increment to outside the range of the simulated ROM, an error interrupt occurs.
Another error interrupt occurs in the event of an illegal instruction op code during simulated execution. The op codes which cause this interrupt are: 11111110, 11111111, 11100011, and all instructions with aPR = 0000 except for 00000000 (NaP).
