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Microcontroller Programming and Interfacing Texas Instruments MSP430 by Daniel J. Pack, Steven F. Barrett

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9.6. USB MODULE 309
TXData++; //Increment TXData
UCB0IFG &= ˜UCSTPIFG;
//Clear stop condition int flag
break;
case 10: break; //Vector 10: RXIFG
case 12: //Vector 12: TXIFG
UCB0TXBUF = TXData; //TX data
break;
default: break;
}
}
//***********************************************************************
9.6 USB MODULE
Figure 9.8 shows the overall USB module of the MSP430.The power for the module is provided by
the VBUS as shown in the figure.The PHY unit in the middle of the figure represents the transceiver
connected to the outside world; the 48 MHz PLL block is used to supply the clock signal to the
PHY unit. The box showing on the right connected to the PHY unit is responsible to configure the
USB module using the USB control registers, manage the buffer used by the module with the help
of the USB Buffer Manger (UBM), and monitor the communications using the Serial Interface
Engine (SIE). We discuss these subsystems of the USB module next.
The MSP430’s USB module is designed to adhere the USB 2.0 specifications. The physical
port used for the USB connection is port U, which can also be programmed as a general purpose
input/output port using the PUSEL bit (1-USB, 0-I/O). The USB SIE is responsible to follow
the USB packet protocol by decoding or creating packet ID, testing or generating cycle redundancy
check values, and checking or triggering synchronization of packets. It is also responsible for required
serial-to-parallel and parallel-to-serial conversions. The USB UBM controls the interface between
SIE and the USB buffers. There are two sets of eight input and output USB buffers in addition to a
setup buffer. Each buffer is configured to specify input/output type, buffer address, buffer size, and
data packet byte count using buffer control registers. The USB module is equipped to detect any
suspended activities on the USB line to resume the communication as well as to wake up MSP430
using the USB line. The module can also be configured to operate based on interrupts - there are 26
interrupts associated with the USB module.
9.7 RF COMMUNICATION USING MSP430
The MSP430 with its ability to operate on a low power budget can easily be connected to a wireless
network of microcontrollers.The primary use of the wireless communication for MSP430 has been
in utility company applications where energy meter values were remotely read, but the number of

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