dsPIC30F Family Reference Manual
DS70067C-page 20-14 © 2004 Microchip Technology Inc.
20.3.3 SPI Error Handling
When a new data word has been shifted into SPIxSR and the previous contents of SPIxRXB
have not been read by the user software, the SPIROV bit (SPIxSTAT<6>) will be set. The module
will not transfer the received data from SPIxSR to SPIxRXB. Further data reception is disabled
until the SPIROV bit is cleared. The SPIROV bit is not cleared automatically by the module and
must be cleared by the user software.
20.3.4 SPI Receive Only Operation
Setting the control bit, DISSDO (SPIxCON<11>), disables transmission at the SDOx pin. This
allows the SPIx module to be configured for a Receive Only mode of operation. The SDOx pin
will be controlled by the respective port function if the DISSDO bit is set.
The DISSDO function is applicable to all SPI Operating modes.
20.3.5 Framed SPI Modes
The module supports a very basic framed SPI protocol while operating in either Master or Slave
modes. The following features are provided in the SPI module to support Framed SPI modes:
• The control bit, FRMEN (SPIxCON<14>), enables Framed SPI modes and causes the SSx
pin to be used as a frame synchronization pulse input or output pin. The state of the SSEN
(SPIxCON<7>) is ignored.
• The control bit, SPIFSD (SPIxCON<13>), determines whether the SSx
pin is an input or an
output (i.e., whether the module receives or generates the frame synchronization pulse).
• The frame synchronization pulse is an active high pulse for a single SPI clock cycle.
The following two framed SPI modes are supported by the SPI module:
• Frame Master Mode: The SPI module generates the frame synchronization pulse and
provides this pulse to other devices at the SSx
pin.
• Frame Slave Mode: The SPI module uses a frame synchronization pulse received at the
SSx
pin.
The Framed SPI modes are supported in conjunction with the Master and Slave modes. Thus,
the following four framed SPI configurations are available to the user:
• SPI Master Mode and Frame Master Mode
• SPI Master Mode and Frame Slave Mode
• SPI Slave Mode and Frame Master Mode
• SPI Slave Mode and Frame Slave Mode
These four modes determine whether or not the SPIx module generates the serial clock and the
frame synchronization pulse.
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