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The terminal block pinout is given in Table 8.

Table 8. Terminal Block Pinout

TERMINAL NAME

FUNCTION

+5VA

5V analog power-supply output

IN1

–

Channel 1 negative input

IN1+

Channel 1 positive input

REF+

Positive reference input

IN2

–

Channel 2 negative input

IN2+

Channel 2 positive input

REF

–

Negative reference input

GND

Board ground

6.4.4

Voltage Reference

The ADS1232REF is designed to operate either ratiometrically or with an external reference. The two

modes are selected using switch SW7.

In the EXT position, the ADS1232 reference inputs are taken from the load cell connectors. In the +5VA

position, the ADS1232 positive reference input comes from the 5V analog supply, and the negative

reference input is connected to ground.

After the switch is placed a filtering network that consists of resistors R14 and R15, bulk capacitor C4,

pass-through capacitors C44 and C45, and filtering capacitors C28, C30, and C31.

6.4.5

Input Shorting Jumpers

The shorted-input noise test for the ADS1232 is best performed with both inputs connected to 2.5V. To

make this test easy to perform, jumpers J7 and J8 are provided.

Jumper J8 shorts the inputs of channel 1 together. Jumper J7 connects the inverting input to a voltage

divider made from R25 and R26, dividing the power supply by 2. This voltage divider electrically

resembles an ideal bridge sensor.

6.5

USB Interface

The USB interface can be used for firmware download or data communications. Its role in firmware

download is discussed in Section 6.6.

The USB interface consists of USB-to-serial converter U4, a Texas Instruments TUSB3410. This device

incorporates a USB interface module, a microcontroller, and a 16550-type UART. Driver software is

available that causes the device to appear as a serial port on the host PC.

The USB interface is powered separately from the rest of the ADS1232REF; it takes power from the USB

line, through linear regulator U3.

The serial port side of U4 is connected to the microcontroller UART signals. To keep the power domains

separate, and to keep the USB and microcontroller sides from inadvertently powering each other, the

UART is connected through isolators U8 and U9.

6.6

Programming Connections

The MSP430 can be programmed via the dedicated JTAG port or the serial bootstrap loader.

The JTAG connector is not factory-installed. The footprint is similar to an edge-card pattern, and accepts a

standard, dual-row 0.100in header mounted on the side of the board. This header is compatible with

MSP430 parallel-port JTAG adaptors.

22

ADS1232REF User

's Guide

SBAU120B

– November 2005 – Revised July 2011

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