Hardware
6.4.3
Input Terminal Block
The input terminal block consists of J4 and J5. It provides connections to all of the analog inputs on the
installed ADS device, and connections to the ADS1x31REF voltage reference network.
The terminal block pinout is given in
.
Table 8. Terminal Block Pinout
TERMINAL NAME
FUNCTION
Negative excitation connected to ground
EXC
–
through installed ADS device
SNS
–
Inverting excitation sense input
SNS+
Noninverting excitation sense input
SIG+
Noninverting input
SIG
–
Inverting input
Positive excitation output (+5V) or positive
EXC+
reference input
6.4.4
Voltage Reference
The ADS1x31REF is designed to operate either ratiometrically or with an external reference. The two
modes are selected using switch SW7.
In the EXT position, the installed ADS reference inputs are taken from the load cell connectors. In the
+5VA position, the installed ADS 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 ADS1x31 devices 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 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
The USB interface consists of USB-to-serial converter U4, a Texas Instruments
. 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 ADS1x31REF; 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
ADS1131REF and ADS1231REF
SBAU175A
–
July 2010
–
Revised August 2011
Copyright
©
2010
–
2011, Texas Instruments Incorporated
