Interfacing the TLC3544 or TLC3548 ADC to the MSP430F149 MCU

Interfacing the TLC3544 or TLC3548 ADC to the MSP430F149 MCU

Trademarks

MSP430 is a trademark of Texas Instruments.

All other trademarks are the property of their respective owners.

1 Introduction

The TLC3544 and TLC3548 are 4- and 8-channel, 14-bit, serial ADCs. Each device has chip select (CS), input clock (SCLK), serial data input (SDI), and serial data output (SDO) pins that can interface directly to a microprocessor. These data converters also feature a programmable end-of-conversion or interrupt (EOC/INT) pin, which can be used to initiate an interrupt service routine on the host processor.

This application report takes advantage of the hardware built into the TLC3544/48 evaluation module. A 20-pin ribbon cable from J12 on the data converter EVM to the microprocessor board is used to carry the necessary interface signals. The EVM’s on-board signal generator provides the analog signals, and W17 allows the user to select either 3.3 V or 5.0 V as the digital I/O voltage. Because the MSP430F149 is a low-voltage device, the EVM’s I/O voltage must be set to 3.3 V before attempting to use this processor.

Ten-pin, dual-row headers were added to the microprocessor boards to accommodate the cable from the data converter EVM. Figure 1 shows the system configuration, and Table 1 shows the connector pinout used.

The sample code (see Section 6) was developed using the Texas Instruments MSP430F149 evaluation board. This simple code example demonstrates how to configure the serial port, initialize the data converter, and process an interrupt (through the EOC/INT pin) from the data converter.

2 TLC3544/48 Evaluation Module

The data converter EVM used for this application report can have either the TLC3544 or the TLC3548 installed at location U9. These are 14-bit, 200-ksps serial analog-to-digital converters with four (TLC3544) or eight (TLC3548) analog input channels.

The TLC3544 and TLC3548 devices operate from a single 5-V analog supply and a 3.3-V or 5.0-V digital supply. The EVM contains regulators that provide all the necessary voltages from a standard 12-V laboratory power supply.

The EVM features a convenient onboard signal generator as well as all the necessary hardware to provide accurate reference voltages to the data converters. Connectors J12, J13, and J14 are

10-pin dual-row headers. These headers simplify interfacing a microcontroller-based system. The shorting bars can be removed from headers J13 and J14, allowing the user to define a custom signal-interface to the EVM.

System I/O voltages, as well as the voltage on the digital portion of the ADC, can be set to either 3.3 V or 5.0 V by changing the position of W17. When W17 is in position 2-3, the I/O voltage is set to 5.0 V. Position 1-2 on W17 lowers the I/O voltage to 3.3 V, which is necessary when running the low-power MSP430™ family of microcontrollers.

Although the onboard signal generator was used as the analog source in this application report, the TLC3544/48 EVM contains a variety of input and output connectors, signal conditioning circuits, and reference voltage options, so that users can define custom analog input conditions. It is even possible to tie the EVM directly into an existing control system – see the TLC3578 Family Evaluation Module User's Guide for complete details.