Datasheet

PGA400 EVM User Guide
TI CONFIDENTIAL – NDA Restrictions
Page 20 of 50
Figure 15. PGA400-Q1 / EVM I2C MUX
5.3 OWI
During final system calibration, the OWI communication method is preferred because it allows
for a three-pin sensor module (Power, GND, VOUT/OWI). The OWI communication method can
be selected in the PGA400-Q1 by either sending the appropriate SPI commands to place the
device in OWI mode, or by issuing the OWI activation pulse and writing software in the 8051 to
switch to OWI mode when the OWI activation pulse is detected. The GUI can be used to create
the OWI activation signal as well as performing the direct SPI writes to place the EVM into OWI
mode. If the GUI is used to send the signals to enter OWI mode, then the EVM will
automatically be configured to route the TX/RX lines from the TI-GER through the OWI
transceiver to the VOUT1 pin.
5.4 UART
An RS-232 transceiver (MAX3221) is present on the EVM that can be used as a debugging
interface from the 8051 MCU to a host PC. The circuit connects the TXD and RXD pins on the
PGA400-Q1 to the MAX3221. The +/-15V RS-232 signals are routed to a standard DB-9
connector on the EVM. The RS-232 circuit is shown below: