Advance Information MC68HC908MR16/MC68HC908MR32 — Rev. 4.0
258 Serial Peripheral Interface Module (SPI) MOTOROLA
Serial Peripheral Interface Module (SPI)
13.7 Error Conditions
These flags signal SPI error conditions:
• Overflow (OVRF) — Failing to read the SPI data register before
the next full byte enters the shift register sets the OVRF bit. The
new byte does not transfer to the r eceive data register, and the
unread byte still can be read. OVRF is in the SPI status and control
register.
• Mode fault error (MODF) — The MODF bit indicates that the
voltage on the slave select pin (SS) is inconsistent with the mode
of the SPI. MODF is in the SPI status and control register.
13.7.1 Overflow Error
The overflow flag (OVRF) becomes set if the receive data register still
has unread data from a previous transmission when the capture strobe
of bit 1 of the next transmission occurs. If an overflow occurs, all data
received after the overflow and before the OVRF bit i s cle ared do es no t
transfer to the receive data register and does not set the SPI receiver full
bit (SPRF). The unread data that transferred to t he receive data register
before the overflow occurred can still be read. Therefore, an overflow
error always indicates the loss of data. Clea r the overflow flag by reading
the SPI status and control register and then reading the SPI data
register.
OVRF generates a receiver/error CPU interrupt request if the error
interrupt enable bit (ERRIE) is also set. M ODF and OVRF can generate
a receiver/error CPU interrupt request. See Figure 13-10. It is not
possible to enable MODF or OVRF individually to generate a
receiver/error CPU interrupt request. However, leaving MODFEN low
prevents MODF from being set.