Datasheet

© 2011 Microchip Technology Inc. DS70143E-page 91
dsPIC30F6011A/6012A/6013A/6014A
14.0 SPI™ MODULE
The Serial Peripheral Interface (SPI™) module is a
synchronous serial interface. It is useful for communi-
cating with other peripheral devices, such as
EEPROMs, shift registers, display drivers and A/D con-
verters, or other microcontrollers. It is compatible with
Motorola's SPI and SIOP interfaces.
14.1 Operating Function Description
Each SPI module consists of a 16-bit shift register,
SPIxSR (where x = 1 or 2), used for shifting data in and
out, and a buffer register, SPIxBUF. A control register,
SPIxCON, configures the module. Additionally, a status
register, SPIxSTAT, indicates various status conditions.
The serial interface consists of 4 pins: SDIx (serial data
input), SDOx (serial data output), SCKx (shift clock
input or output), and SSx
(active-low slave select).
In Master mode operation, SCK is a clock output but in
Slave mode, it is a clock input.
A series of eight (8) or sixteen (16) clock pulses shift
out bits from the SPIxSR to SDOx pin and simultane-
ously shift in data from SDIx pin. An interrupt is gener-
ated when the transfer is complete and the
corresponding interrupt flag bit (SPI1IF or SPI2IF) is
set. This interrupt can be disabled through an interrupt
enable bit (SPI1IE or SPI2IE).
The receive operation is double-buffered. When a com-
plete byte is received, it is transferred from SPIxSR to
SPIxBUF.
If the receive buffer is full when new data is being trans-
ferred from SPIxSR to SPIxBUF, the module will set the
SPIROV bit indicating an overflow condition. The trans-
fer of the data from SPIxSR to SPIxBUF will not be
completed and the new data will be lost. The module
will not respond to SCL transitions while SPIROV is ‘1’,
effectively disabling the module until SPIxBUF is read
by user software.
Transmit writes are also double-buffered. The user
writes to SPIxBUF. When the master or slave transfer
is completed, the contents of the shift register (SPIxSR)
are moved to the receive buffer. If any transmit data has
been written to the buffer register, the contents of the
transmit buffer are moved to SPIxSR. The received
data is thus placed in SPIxBUF and the transmit data in
SPIxSR is ready for the next transfer.
In Master mode, the clock is generated by prescaling
the system clock. Data is transmitted as soon as a
value is written to SPIxBUF. The interrupt is generated
at the middle of the transfer of the last bit.
In Slave mode, data is transmitted and received as
external clock pulses appear on SCK. Again, the inter-
rupt is generated when the last bit is latched. If SSx
control is enabled, then transmission and reception are
enabled only when SSx = low. The SDOx output will be
disabled in SSx mode with SSx high.
The clock provided to the module is (F
OSC/4). This
clock is then prescaled by the primary (PPRE<1:0>)
and the secondary (SPRE<2:0>) prescale factors. The
CKE bit determines whether transmit occurs on transi-
tion from active clock state to Idle clock state, or vice
versa. The CKP bit selects the Idle state (high or low)
for the clock.
14.1.1 WORD AND BYTE
COMMUNICATION
A control bit, MODE16 (SPIxCON<10>), allows the
module to communicate in either 16-bit or 8-bit mode.
16-bit operation is identical to 8-bit operation except
that the number of bits transmitted is 16 instead of 8.
The user software must disable the module prior to
changing the MODE16 bit. The SPI module is reset
when the MODE16 bit is changed by the user.
A basic difference between 8-bit and 16-bit operation is
that the data is transmitted out of bit 7 of the SPIxSR for
8-bit operation, and data is transmitted out of bit15 of
the SPIxSR for 16-bit operation. In both modes, data is
shifted into bit 0 of the SPIxSR.
14.1.2 SDOx DISABLE
A control bit, DISSDO, is provided to the SPIxCON reg-
ister to allow the SDOx output to be disabled. This will
allow the SPI module to be connected in an input only
configuration. SDO can also be used for general
purpose I/O.
Note: This data sheet summarizes features of
this group of dsPIC30F devices and is not
intended to be a complete reference
source. For more information on the CPU,
peripherals, register descriptions and
general device functionality, refer to the
“dsPIC30F Family Reference Manual”
(DS70046).
Note: Both the transmit buffer (SPIxTXB) and
the receive buffer (SPIxRXB) are mapped
to the same register address, SPIxBUF.