Serial Peripheral Interface (Spi) - Digilent chipKIT Pro MX7 Reference Manual

chipKIT™ Pro MX7 Board Reference Manual
Detailed information about the operation of the UART peripherals can be found in the PIC32 Family Reference
Manual, Section 21, UART.
The USB Serial converter is connected to UART1. The MPIDE uses this to communicate with the boot loader. This
can also be used for a serial communications interface between the chipKIT Pro MX7 board and other software
running on a PC. Resistors are used to decouple the USB serial interface and so UART1 can also be used via Pmod
connector JE when not using it to communicate with the USB serial converter.
Note that when using the MPIDE software, devices connected to JE can interfere with the operation of the serial
interface and prevent the MPIDE from successfully downloading sketches to the board. If this happens, disconnect
the external device from JE until the sketch has been downloaded and then reconnect it.
When using the chipKIT Pro MX7 with the MPIDE and the chipKIT system, the UARTs are accessed using the
HardwareSerial facility built into the system. UART1 Pmod port JE, is accessed using the Serial object and
UART2 Pmod port JF, is accessed using Serial1.

10 Serial Peripheral Interface (SPI)

SPI is a four wire synchronous serial interface and SPI devices can operate as either master devices or as slave
devices. The PIC32 microcontroller labels the four SPI signals as Slave Select (SS), Serial Data Out (SDO), Serial Data
In (SDI), and Serial Clock (SCK). A master device transmits SS, SDO, SCK, and receives SDI. A slave device receives SS,
SDI, SCK, and transmits SDO. The SS signal is used to enable the slave device, and this signal is only significant for
slave devices. A master device can use any general purpose I/O pin to generate SS to enable the slave.
An SPI transaction begins with the master device bringing SS low. When the slave sees SS go low it becomes
enabled and waits for the master to send data. The master shifts data out on SDO and simultaneously shifts data in
on SDI. The slave device receives data from the master on its SDI pin and simultaneously sends data to the master
on its SDO pin. Each time the master sends a byte to the slave, it simultaneously receives a byte from the slave.
The PIC32MX795 microcontroller provides four Serial Peripheral Interfaces. The chipKIT Pro MX7 supports use of
three ports: SPI1, SPI3, and SPI4. These are accessed using Pmod ports JD, JE, and JF.
The following gives the mapping between SPI signals and connector pins:
 SS1 JD-01
 SDO1
JD-02
 SDI1
JD-03
 SCK1
JD-04
 SS3 JE-01
 SDO3
JE-02
 SDI3
JE-03
 SCK3
JE-04
 SS4 JF-01
 SDO4
JF-02
 SDI4
JF-03
 SCK4
JF-04
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