CNC machine tool and computer communication circuit diagram design

CNC machine tool and computer communication circuit diagram design

1.RS-485/RS-232 interface circuit

The main function of the RS-485/RS-232 interface circuit is to realize the conversion between RS-485 level and RS-232 level, as shown below:

Figure 1 RS-485/RS-232 interface circuit

MAX232 is an RS driver chip that can convert between RS-232 levels and TTL levels. MAX485 is an RS-485 driver chip that can convert between RS-485 levels and TTL levels. The parameters of MAX485 are the same as SN75176. CD4019 is a 2-to-1 data selector, because the microcontroller AT89C2051 has only one serial communication port, and the communication node requires two serial ports. In order to save costs, a data selector is used to switch the serial communication port.

CD4019 is a four-AND-OR gate 2-to-1 data selector. The figure below is its internal logic diagram.

Figure 2 CD4019 internal logic diagram

2. Microcontroller and watchdog

The data of RS-485 and RS-232 interface must pass through the microcontroller, as shown below

Figure 3 Microcontroller and watchdog circuit

As shown in the picture above, the microcontroller uses AT89C2051. The crystal oscillator uses 11.0592MHz, which is selected to meet the baud rate of 9600/s. DIP8 is an 8-bit address switch, which is used as the address code of the communication node. Up to 256 address codes can be programmed. MAX813L is a watchdog The chip can generate a reset signal during power-on, power-down, communication and when the voltage drops.

3. Power circuit

The communication cable of this system uses 3 cores with shielding, two of which are RS-485 signal lines and one is a power line, which provides +9V DC current to each node. Each communication node reduces it to +5V. As shown below;

Figure 4 Microcontroller power supply circuit diagram

L1 is a 100uH inductor with large AC impedance to prevent high-frequency interference on the bus from entering the node circuit. The diode VD1 has two functions: one is to reduce the input voltage of the integrated voltage stabilizing circuit 7805; the other is to prevent the charge stored on the capacitor C1 from being released to the bus when the bus is powered off. Capacitors C1 and C2 are filter capacitors. 7805 is a +5V integrated voltage regulator circuit. C3 and C4 are decoupling capacitors. The light-emitting diode VD2 is the power indicator light, and R1 is the current limiting resistor of VD2.