This article mainly verifies the level of the control pin (ENA/IN1/IN2/ENB/IN3/IN4) of the L298P motor driver chip when it is floating. Can it be compared with 3.3V logic? The controllers are directly connected (small current/small-interference motor, optocoupler isolation can be used to reduce costs), and the experimental platform uses the MTU_GO_V1_1 experiment board of “Cracking a Creative Electronics Factory”. The basic drawings are shown in Figure 1. 图1 L298P输入逻辑原理图
When Vss (logic power supply) and Vs (motor power supply) are both 5V input, room temperature is 25 °C (the following tests are based on this test environment, if there is any difference, will be explained separately). Pin triode and pull-up resistor are present. 1 Transistor does not exist. Pull-up resistor exists. 2 Triode and pull-up resistors are not present. 3 功耗方面，①和②约为44mA @5V，③约为7mA @5V。
Only ENA and ENB are pulled up to 5.0V through 10K resistors, respectively. /IN2/IN3/IN4 are all floating, and the logic level test results of each control pin are shown in the following table.
Only when ENA and ENB are pulled up to GND through 10K resistors, IN1/IN2/IN3/IN4 are all left floating. The logic level test results of each control pin are shown in the following table.
Based on the above actual test, there is no pull-up resistor inside the L298P, because when the control pin is left floating, the measured voltage is less than 400mV (a jump value), so use a 3.3V logic. The controller is directly connected to the L298 chip and there is no problem. We can also get more conclusive information from L298 datasheet, ViL<1.5V, VIH>2.3V, as shown in the following table.