
Serial Peripheral Interface Module (SPI)
Error Conditions
MC68HC(7)08LN56 — Rev. 2.0
General Release Specication
MOTOROLA
Serial Peripheral Interface Module (SPI)
177
NONDISCLOSURE
AGREEMENT
REQUIRED
implies that a back-to-back write to the transmit data register is not
possible. The SPTE indicates when the next write can occur.
11.8 Error Conditions
The following 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 receive 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.
11.8.1 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. The bit 1 capture strobe occurs
an overflow occurs, all data received after the overflow and before the
OVRF bit is cleared does not transfer to the receive data register and
does not set the SPI receiver full bit (SPRF). The unread data that
transferred to the receive data register before the overflow occurred can
still be read. Therefore, an overflow error always indicates the loss of
data. Clear 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. When the DMAS bit is low, the
SPRF, MODF, and OVRF interrupts share the same CPU interrupt
vector. When the DMAS bit is high, SPRF generates a receiver DMA
service request, and MODF and OVRF can generate a receiver/error
MODF or OVRF individually to generate a receiver/error CPU interrupt