Type1: CPU only
Type2: All components on the PCB and RC stickers
Type3: Complete solder testing out of the box
This product is a 4-bit CPU, which is made of 9 kinds of 74 series small-scale integrated circuit chips. Through the display at the circuit level, you can intuitively understand the operation process of the CPU, which is convenient to complete the basic learning of digital circuit design. It is useful for teaching or self-learning research. Intuitive guidance.
This product requires users to have certain electronic welding ability and basic knowledge of digital circuits.
Please use this product in conjunction with the Zhihu tutorial, it will be very helpful for the understanding and learning of the two courses of digital circuits and microcomputer principles.
Newly designed SMT version
Installation Introduction
This model is the SMT version, the PCB board and the mounting of SMD capacitors, SMD resistors and LEDs have been completed, which greatly reduces the welding workload of components, but still requires your patience. Quite the version you can get from other channels, we provide this version with a lot of practical improvements.
Tools needed: soldering iron, solder, tweezers
The two purchased PCB boards are shown in the figure below, which are the ROM board and the CPU board.
Soldering of CPU board
Components to be welded: 74 series chips
(74HC14, 74HC10, 74HC32, 74HC74, 74HC283, 74HC283 (with seat), ) each
74HC153 two 74HC161 four;
Three polar capacitors 10uf;
Two toggle switches;
Two key switches;
One four-digit DIP switch;
Two looper female headers;
One USB connector;
Recommended welding sequence: chip (74HC283 is last) ¡æ USB connector ¡æ looper female header, four-position DIP switch, toggle switch ¡æ key switch, female header
¨çChip welding
Now tin the pads on one side ¡æ Hold the chip with tweezers (pay attention to the correct orientation of the chip) and solder the tinned side, and then solder the other side
Soldering of ROM board
Components to be welded: 74 series chips
74HC540 one
74HC138 two
16 8-bit DIP switches;
Two looper pin headers;
Recommended welding sequence: chip (74HC283 is last) ¡æ bent pin header ¡æ 8-bit DIP switch
After the installation is complete, use the machine language to complete the toggle according to the instruction set (Instruction Set)
Emulator
Next, let`s take a look at an emulator. At this moment, you don`t need to understand all the details in the emulator. In the follow-up description, after each part is understood, come back and re-read this dynamic simulation program, you can fully understand understand.
Now, when you look at the running graph of this simulation program, all you need to know are the following:
The red line indicates that the level on the line is high (5V) at this time, and the blue line indicates that the level is low (ie 0V).
The whole system is driven by the CLOCK pulse, and RESET is active at low level, that is, after RESET is pulled low, all data in the system is cleared and restarted
If you have already learned the basics of digital circuits, you should also try to remember and understand the following points.
The four 74HC161 are registers A, B, C, D, which can be used to store 4 bits of data respectively
The output of the third register C is used to output a 4-bit level to drive the LED
The output of the fourth register D is used for the decoding of the instruction, that is, A0-A3 (Address0-Address3) as the address bus
Two 74HC153s form a 4-bit quad data selector, which is used to select which 4-bit data is used as the addend A for the subsequent four-bit full adder. Among them, the 4-bit data of the third channel comes from the 4-bit DIP switch (ie input), and the fourth channel is not connected and discarded.
74HC283 is a four-way full adder. Its first addend comes from the data selection channels of the two 74HC153, and the second addend comes from the lower 4 bits of the instruction data (ie D3-D0). The data involved in the operation in the instruction is also called immediate. The summation result of the full adder will be output to the 4-bit registers A, B, C, and D. The choice of which register to store the result is completely determined by the LOAD (~LD) signal at the input of each register. Please note that LOAD is Active low, this is the most important part of the control bus in the result of subsequent instruction decoding.
The full adder has an overflow bit to output Carry, but it cannot remember whether the last calculation result overflowed, so a D flip-flop is needed as an overflow flag bit to remember whether the last summation result overflowed, and send it to the decoder instruction.
All the combinational circuits represented by gate circuits in the figure are a complete instruction decoder. It uses the upper 4 bits of the instruction (ie D7-D4) and the overflow flag bit as the input of the decoder, and controls the four registers. The load (LD) and the A and B of the two data selectors are used as outputs, which is a typical control bus.
Why do this?
Although the function is simple, but a complete CPU, the sparrow is small and complete
Using 9 kinds of small-scale integrated circuit chips (74 series), the basic learning of digital circuit design can be completed, and the principle of circuit working layer can be thoroughly and intuitively understood.