The method proposed in this paper can be used to evaluate one-wire devices that carry out pulse-width coded communication through a PC serial port , and monitor communication errors such as parity and response. The hardware interface with the PC is the MAX232 driver / receiver. The slave device in this example is a TMP141 temperature sensor from Texas Instruments. Using the 4 programmable addresses of TMP141 determined by A0 and A1 (see Figure 1), this circuit can be expanded to have 4 sensors on the same bus.
The main icon of this method uses the built-in time controlled by the RS-232 baud rate. Most communications require 3 "bit codes": (start bit), data (bit 0) and data (bit 1) (see table and figure 2). Use mscomm of Visual Basic to configure the PC COM port to output 8 data bits, no parity, 1 stop bit, and no flow control. The COM port data bit setting and baud rate determine the bit code width. By changing the baud rate between bits, different pulse width codes are obtained.
Programming the PC COM port baud rate will cause a delay between 20 and 30 ms. Because the slave device does not have a timeout event, this delay is not a problem. However, delays can complicate reading the output on a logic analyzer. The Visual Basic program controls the two-way communication to the TMP141 sensor. Use the program to read and program internal registers.
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