Circuit design of network signal conversion system based on CO2128

　　In order to realize the signal conversion needs without the computer system, this paper proposes a bus signal conversion design based on CO2128 and DSP, and gives the hardware and software design methods of the signal conversion device. The DSP used in this design is TI's TMS320LF2407, which has SCI and CAN bus interfaces and can quickly realize the conversion of the two signals through a simple program. TMS320LF2407 uses high-performance static CMOS technology and has a power supply voltage of 3.3 V, so it can reduce the power consumption of the controller.

　　Circuit principle: The execution speed of 30MIPS shortens the instruction cycle to 33 ns, thereby improving the real-time control capability of the controller. However, when designing the network interface, pay close attention to the signal line layout of the PCB board. Usually, the network transformer should be placed as close as possible to the DM9161 and the RJ45 socket, and the distance from the DM9161 should not exceed 20 mm; the 50Ω terminal resistor should be placed as close as possible to the network transformer and the RX and TX pins of the DM9161. The 50-ohm resistor and the grounding capacitors of the RX and TX should be placed near the DM9161, not more than 10 mm; the 25 MHz crystal should not be placed around important signals. The routing from the RX of the DM9161 to the network transformer and RJ45 must be symmetrical, direct, parallel and close. Do not go at right angles or 45 degrees. When laying out the RX and TX, avoid using vias. The RX, TX, CLK and power routing are required to be as short as possible. RX and TX cannot cross, and the distance should be more than 3 mm. It is best to lay a ground wire between them. Do not run any digital lines from the RX and TX pairs of the DM9161 to the RJ45. Keep these two pairs of signals away from other signals and the ground. There must be no ground or power plane under the network transformer and RJ45. All RJ45 terminal pins (4, 5, 7, 8) and the network transformer must be close together and grounded through a resistor and a 0.01 uF/2 kV capacitor. The BANDGAP resistor must be placed as close to pins 47 and 48 as possible (no more than 3 mm). Avoid having any high-speed signals near this resistor (must be greater than 3 mm to the crystal oscillator).