Memory control circuit

TL;DR: In this paper, the authors propose a means to a memory control circuit to set a prescribed memory area of a RAM under a writing unable state and switch the working mode to a read-only process.

Abstract: PURPOSE:To realize the program debugging without using any special debugging device by adding a means to a memory control circuit to set a prescribed memory area of a RAM under a writing unable state and switches the working mode to a read-only process. CONSTITUTION:When a soft switch 19 is turned on with a hard switch 15 is kept turned on, a memory area 1a allocated to address spaces 60000H-7FFFH of a RAM 1 is defined as a read-only state. Thus the access to a ROM 2 of a CPU 3 is equal to an access to the area 1a of the RAM 1 when a program stored in the ROM 2 is written into the area 1a and switches 15, 19 and 20 are turned on respectively. Thus the program of the ROM 2 shifted to the area 1a can be debugged under the control of a personal computer.