dsPIC30F Family Reference Manual
DS70067C-page 20-2 © 2004 Microchip Technology Inc.
20.1 Introduction
The Serial Peripheral Interface (SPI) module is a synchronous serial interface useful for
communicating with other peripheral or microcontroller devices. These peripheral devices may
be Serial EEPROMs, shift registers, display drivers, A/D converters, etc. The SPI module is
compatible with Motorola's SPI and SIOP interfaces.
Depending on the variant, the dsPIC30F family offers one or two SPI modules on a single device.
SPI1 and SPI2 are functionally identical. The SPI2 module is available in many of the higher pin
count packages (64-pin and higher), while the SPI1 module is available on all devices.
The SPI serial port consists of the following Special Function Registers (SFR):
• SPIxBUF: Address in SFR space that is used to buffer data to be transmitted and data that
is received. This address is shared by the SPIxTXB and SPIxRXB registers.
• SPIxCON: A control register that configures the module for various modes of operation.
• SPIxSTAT: A status register that indicates various status conditions.
In addition, there is a 16-bit shift register, SPIxSR, that is not memory mapped. It is used for
shifting data in and out of the SPI port.
The memory mapped SFR, SPIxBUF, is the SPI Data Receive/Transmit register. Internally, the
SPIxBUF register actually comprises of two separate registers - SPIxTXB and SPIxRXB. The
Receive Buffer register, SPIxRXB, and the Transmit Buffer register, SPIxTXB, are two unidirec-
tional 16-bit registers. These registers share the SFR address named SPIxBUF. If a user writes
data to be transmitted to the SPIxBUF address, internally the data gets written to the SPIxTXB
register. Similarly, when the user reads the received data from SPIxBUF, internally the data is
read from the SPIxRXB register. This double-buffering of transmit and receive operations allows
continuous data transfers in the background. Transmission and reception occur simultaneously.
The SPI serial interface consists of the following four pins:
• SDIx: serial data input
• SDOx: serial data output
• SCKx: shift clock input or output
•SSx
: active low slave select or frame synchronization I/O pulse
Note: In this section, the SPI modules are referred together as SPIx or separately as SPI1
and SPI2. Special Function registers will follow a similar notation. For example,
SPIxCON refers to the control register for the SPI1 or SPI2 module.
Note: The user cannot write to the SPIxTXB register or read from the SPIxRXB register
directly. All reads and writes are performed on the SPIxBUF register.
Note: The SPI module can be configured to operate using 3 or 4 pins. In the 3-pin mode,
the SSx
pin is not used.
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