JPS5858701B2 - How to start a microprocessor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for starting up a microprocessor, and more particularly, to a method for starting up a microprocessor, and more particularly, to start up a microprocessor, and more particularly, to start up a microprocessor by starting up memory in a RAM (Random Access Memory) area and a ROM (Read Only Memory) area immediately after power-on of the microprocessor. It concerns address translation.

Generally, the start address after a microprocessor is powered on is often the lowest or highest address in the memory space.

For example, in the case of an 8-bit microprocessor whose start address after power-on is address O, the control program for the processor system is often stored in a ROM starting from memory address zero.

However, if the storage address of the jump destination address at the time of an interrupt exists in the above ROM area and the jump destination address is changed in the middle of the control program, or if the memory address from address 0 is used as the RAM area, the memory space If the RAM area and ROM area within the memory can be rearranged, an efficient memory space can be constructed.

In view of the above points, the present invention provides a RAM area containing a memory start address and a RAM area containing a control program for the microprocessor system when the microprocessor is powered on.
The present invention provides a method for executing a control program by exchanging the addresses of the OM area, and returning the addresses of the RAM area and ROM area during the program to continue the program in the normal memory space.

Hereinafter, the present invention will be explained based on illustrated embodiments.

FIG. 1 is a block diagram for explaining one embodiment of the present invention, and shows a memory area conversion section of an 8-bit microprocessor.

The memory capacity is 64 bytes, and address signal lines for memory access are ABO to AB15.

In this example, the memory space of 64 bytes is 3 RAMs.
It is divided into four areas: one area and one ROM area.

40 in the figure is the first RAM area from memory address oooo to 3FFF, and 41 is memory address 4000 to 7.
A second RAM area up to FFF, 42 a ROM area up to memory addresses 8000-BFFF, and 43 a third RAM area up to memory addresses cooo-FFFF.

10°11, 12 and 13 are the first RAM areas, respectively;
This is an address control gate circuit for selecting a second RAM area, a ROM area, and a third RAM area.

50 is a memory area conversion flip-flop circuit, which receives a reset signal (RE) when the processor system is powered on.
SETN).

Since the start address of the microprocessor used in this embodiment when powered on is oooo, the memory area selection signal is output from the address control gate circuit 10.

20 in the figure is the output signal of the address control gate circuit 10 and the Q of the memory area conversion flip-flop circuit 50.
Since it is an AND gate circuit that ANDs the output signals,
The memory area selection signal is not input to the fourth RAM area.

On the other hand, 30 is an OR gate of the output signal of the address control gate circuit 12 and the output signal of the memory area conversion flip-flop circuit 50, so the memory area selection signal is input to the ROM area and stored in the ROM area. The microprocessor operates according to the program.

For example, if the program in the ROM area has the following format, the JMP instruction (3-byte instruction) at memory address 8000
, the program counter of the microprocessor is changed from oooo to 8003, and the OUT instruction (2-byte instruction) at memory address 8003 causes the set signal (EXCHGN) to be output.The output state of the memory area conversion flip-flop circuit 50 is Invert.

The output signal of the flip-flop circuit 50 is the AN
The data is input to the D gate circuit 20 and the OR gate circuit 30, and the memory addresses of the first RAM area and ROM area are swapped again.

On the other hand, the processor system has memory address 8005
It will operate according to the program from.

In other words, the start address at power-on is oooo
However, the memory area conversion unit of this embodiment allows the program to run smoothly.

Starting from , memory addresses oooo to 7FFF and C000 to FFFF can be used as a RAM area.

FIG. 2 is a block diagram for explaining another embodiment of the present invention, showing a memory area converter.

In the figure, γ0. γ1. γ2. γ3 is an AND gate circuit,
80 and 81 are OR gate circuits, and the other parts are the same as in FIG.

In the embodiment of FIG. 2, the memory address ooo
The first RAM area 40 of o to 3FFF is connected to the memory area conversion flip-flop circuit 50 by the set signal (EXCHG
memory address 8000-B until set by
Read/written as FFF.

In this case, the program that controls the processor system is written to the RAM area 40 after power-on, and
When the program in the OM area 42 outputs a set signal to the memory area conversion flip-flop circuit 50,
Control of the microprocessor is transferred from the program in the ROM area to the program in the first RAM area.

As is clear from the above description, the present invention uses one flip-flop circuit that is automatically turned on at power-on to store a RAM containing a memory start address.
By exchanging the memory addresses of the ROM area containing the area and the program, the processor operates according to the program written in the ROM.
This has the excellent feature that the RAM area can be set regardless of the start address of the microprocessor.

[Brief explanation of drawings]

1 and 2 are block diagrams for explaining the present invention in detail, respectively. 10-13...address control gate circuit, 20
゜70~γ3...AND gate circuit, 30,8
0゜81...OR gate circuit, 50...
・Memory area conversion flip-flop circuit, 40...
..." RAM area, 41... Second RAM
Area, 42...ROM area, 43...
@3 RAM area.

Claims (1)

[Claims] 1. In a microprocessor system where the start address at power-on starts from the lowest or highest memory space, a random access memory is used in the memory space including the lowest or highest memory space, and some other spaces are used. When using read-only memory,
The address of the random access memory area and the address of the read-only memory area are exchanged using one flip-flop circuit configured to turn on automatically when the power is turned on. Activation of a microprocessor characterized in that the processor is operated according to a program written in a memory, and the flip 7171 circuit is turned off by the program to restore the addresses of the random access memory area and the read-only memory area. Method.