NXP Semiconductors TWR-56F8400 User Manual

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NXP Semiconductors TWR-56F8400 User Manual Manual pdf 14 page image

TWR-56F8400 User’s Manual Page 14 of 352.3.6 Tower Elevator ConnectorsThe TWR-56F8400 board features two expansion card-edge connectors that interface to Elevatorboards in a Tower System: the Primary and Secondary Elevator connectors. The Primary Elevatorconnector, comprised of sides A and B, is utilized by the TWR-56F8400 board, while the SecondaryElevator connector only makes connections to ground (GND). Table 7 in Appendix A – Tower ElevatorConnector Pin Functions lists the pin functions for the Primary Elevator Connector.2.3.7 Thermistors as Analog InputsThe TWR-56F8400 board provides four thermistors (RT1-4) near the corners of the board that can beused as single ended or differential analog inputs to the MC56F84789 DSC as can be seen on sheet 6 ofthe schematic. In addition to each thermistor there is a resistor between the thermistor and P3_3V andanother resistor between the thermistor and ground. The thermistors are all 10K ohm parts but theassociated divider chain uses different resistors. This makes the voltage across the thermistor larger orsmaller and provides the ability to try the different gain settings on the analog channels. All fourthermistor circuits are designed to provide useable differential inputs over the temperature range of90˚C to -20˚C. RT2 and RT4 both give a differential voltage of ~1.65V at 25˚C. RT1 gives a differentialvoltage of 0.10V and RT3 gives a differential voltage of 0.28V at 25 ˚C.In addition to the thermistor voltage divider chain each thermistor has a 0.1 uF capacitor in parallel.Each thermistor circuit also has a header that allows the thermistor to be disconnected from theanalog inputs to the DSC. If a user wishes to apply an external analog value these headers may beremoved and the external analog signal attached to the DSC side of the headers. Finally, each analoginput to the DSC has a 100 ohm series resistor and a 2200 pF capacitor as a low pass filter. This helpsprotect the DSC from electrostatic discharges and lowers the impedance of the analog signal so that itcan be sampled with less noise.2.3.8 CAN TransceiverThe TWR-56F8400 board has a CAN transceiver circuit that may be connected to the CAN pins of theDSC. The CAN transceiver (U503) can be connected to the GPIOC11/CANTX/SCL1/TXD1 andGPIOC12/CANRX/SDA1/RXD1 pins of the DSC through the header at J16. Installing a shunt from pin 1 topin 2 connects the TXD nets and installing a shunt from pin 3 to pin 4 connects the RXD nets. Note thatthe GPIOC11/CANTX/SCL1/TXD1 and GPIOC12/CANRX/SDA1/RXD1 nets also go to the primary elevatoredge connector (J500A) pins B41 and B42 and to the Auxiliary connector (J502) pins 15 and 17. Whenusing these nets for CAN communications care must be taken that these nets are not driven from theseother connectors.The transceiver is capable of running from 3.3V and is powered by the P3_3V/5V power rail. Thetransceiver output is connected to header J13 with CANH connected to pin 4 and CANL connected to