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SPI Register Descriptions (SPI_BASE = $1FFFE8)
MOTOROLA
Serial Peripheral Interface (SPI)
11-25
Preliminary
11
Control Register is set also. This bit may not be cleared.
0 = Receive Data Register not full
1 = Receive Data Register full
11.11.1.12 Overflow (OVRF)—Bit 2
This read-only flag is set if software does not read the data in the Receive Data Register
before the next full data enters the Shift Register. In an overflow condition, the data
already in the Receive Data Register is unaffected, and the data shifted in last is lost. Clear
the OVRF bit by reading the SPI Status and Control Register with OVRF set and then
reading the Receive Data Register. This bit may be cleared using the proper software
sequence.
0 = No overflow
1 = Overflow
11.11.1.13 Mode Fault (MODF)—Bit 1
This read-only flag is set in a slave SPI if the SS pin goes high during a transmission with
the MODFEN bit set. In a master SPI, the MODF flag is set if the SS pin goes low at any
time with the MODFEN bit set. Clear the MODF bit by writing a one to the MODF bit
when it is set. The delayed bit results in only the OVRF interrupt being enabled by the
ERRIE bit. This enabling generates receiver/error interrupt requests.
0 = SS pin at appropriate logic level
1 = SS pin at inappropriate logic level
11.11.1.14 SPI Transmitter Empty (SPTE)—Bit 0
This read-only flag is set each time the Transmit Data Register transfers a full data length
into the Shift Register. SPTE generates an interrupt request if the SPTIE bit in the SPI
Control Register is set also. This bit may be cleared using the proper software sequence.
0 = Transmit Data Register not empty
1 = Transmit Data Register empty
Note:
Do not write to the SPI Data Register unless the SPTE bit is high.
11.11.2 SPI Data Size and Control Register (SPDSCR)
This read/write register determines the data length for each transmission. The master and
slave must transfer the same size data on each transmission. A new value will only take
effect at the time the SPI is enabled (SPE bit in SPSCR register set from zero to one). In