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MSP430f2618 UART USCI_A0

ganesh shankar vidharthi
Prodigy 60 points
Other Parts Discussed in Thread: MSP430F2618, MAX3232

I have wrote code for MSP430f2618 UART USCI_A0  module .

I have one PCB that has RS232 port. PCB has two wires for RX an TX thar connects to  2 pins P3.4 and P3.5 on MSP430 MCU respectively.

MSP --------->>>(TX and RX pins P3.4 and P3.5)------------->>> PCB----->>>(RS232 PORT using cross serial cable  )-------->>>PC(serial PORT)

Above  configurations works fine.

BUT instead of using PCB, I connected MSP430 MCU to PC (serial port) using straight serial Cable .

This configuration doesnot works. Why?

Please help  me

  • 0
    Expert 1480 points

    Hello,

    I think it has to do with the interface specification on physical layer for RS232.

    Maybe you should check the voltage levels of the PC serial interface to  check this.

    Wiki (see last paragraph):

    The RS-232 standard defines the voltage levels that correspond to logical one and logical zero levels for the data transmission and the control signal lines. Valid signals are plus or minus 3 to 15 volts; the ±3 V range near zero volts is not a valid RS-232 level. The standard specifies a maximum open-circuit voltage of 25 volts: signal levels of ±5 V, ±10 V, ±12 V, and ±15 V are all commonly seen depending on the power supplies available within a device. RS-232 drivers and receivers must be able to withstand indefinite short circuit to ground or to any voltage level up to ±25 volts. The slew rate, or how fast the signal changes between levels, is also controlled.

    For data transmission lines (TxD, RxD and their secondary channel equivalents) logic one is defined as a negative voltage, the signal condition is called marking, and has the functional significance. Logic zero is positive and the signal condition is termed spacing. Control signals are logically inverted with respect to what one sees on the data transmission lines. When one of these signals is active, the voltage on the line will be between +3 to +15 volts. The inactive state for these signals is the opposite voltage condition, between −3 and −15 volts. Examples of control lines include request to send (RTS), clear to send (CTS), data terminal ready (DTR), and data set ready (DSR).

    Because the voltage levels are higher than logic levels typically used by integrated circuits, special intervening driver circuits are required to translate logic levels. These also protect the device's internal circuitry from short circuits or transients that may appear on the RS-232 interface, and provide sufficient current to comply with the slew rate requirements for data transmission.

    Regards Marco

  • 0 in reply to Marco
    Guru 227245 points

    Marco said:
    Because the voltage levels are higher than logic levels typically used by integrated circuits, special intervening driver circuits are required to translate logic levels

    Or in short words: to interface an MSP (or mos tother microcontrollers with TTL UART signal levels) with a PC COM port, you'll need an level shifter like the MAX3232, which can generate the required negative voltage, inverts the levels and can accept the possibly high input voltages.

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