INVASION OF THE CHIPKIT MAX32 - Nuts & Volts Magazine

DESIGN CYCLE■ PHOTO 2. The chipKIT Network Shield complements thePIC32MX795F512L's internal communications subsystemsby providing the physical means to access them.PHY portion of the Network Shield is graphically depictedin Schematic 3.The MCP2551 CAN transceiver circuits are inked inSchematic 4. Note that the transceivers require a +5.0 voltsupply. If you’re CAN challenged, those 120Ω resistors areCAN termination resistors. The termination resistors resideat each end of the CAN network. Portals for accessing theI 2 C bus and an onboard 24LC256 I 2 C EEPROM are alsorevealed by the installation of the Network Shield. If youplan to use your Shield in an I 2 C network, you must usebus pull-up resistors in accordance with the I 2 Cspecification. Note the 2.2KΩ pull-up resistors on the24LC256 SCL and SDA lines in Schematic 5.To utilize the PIC32MX795F512L’s internal RTCC(Real Time Clock Calendar), all we really need from ahardware point of view is a 32.768 kHz clock source. TheNetwork Shield is loaded with a 32.768 kHz crystaloscillator which we can use to keep up with the time anddate. The Network Shield is equipped with a pair of USBinterfaces. The Max32 can be configured as a USB host, aUSB device, or a USB OTG device. When configured toact as a USB host, the Network Shield must have a meansof supplying +5.0 volts at the USB host interface. Take alook at Schematic 6. The TPS2051B is a solid-state powerswitch that is under the control of the Max32’s VBUSONsignal. When the TP2051B’s EN input is logically high,VCC5V0 flows to the TP2051B’s OUT pin. The TP2051B’sOUT pin voltage is manually directed to one of the USBinterfaces via a jumper. An overcurrent condition isreported to the PIC32MX795F512L via the TP2051B’sactive-low OC pin. We’ve established one thing forcertain: the Max32 loaded with a Network Shield isdefinitely not a piece of junk. The Max32/Network Shieldcombination has the ability to communicate with mostany embedded or cloud-based computing platform. TheMax32 can even talk to your car.BILINGUAL SILICONThe Max32 was designed to support Arduino with aMicrochip 32-bit microcontroller. However, the Max32and the Network Shield combine to form a perfect PICdevelopment platform. If you want to use the Max32 as adevelopment tool, you’ll need to take control of the■ SCHEMATIC 3. ThechipKIT Network Shieldholds everything thePIC32MX795F512L'sEthernet MAC needs tobecome a full-fledgedEthernet node.October 2011 59