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Serial Communication Modules
MOTOROLA
MPC801 USER’S MANUAL
16-25
16
16.3.2.4.5 SPI Event Register.
The 8-bit read/write SPI event register (SPIER) is used to
generate interrupts and report events recognized by the serial peripheral interface. When an
event is recognized, the serial peripheral interface sets the corresponding bit in the SPIER.
Interrupts are only generated by this register for E or F events and can be masked in the
SPIMR. A bit is cleared by writing a 1 (writing a zero has no effect) and more than one bit
can be cleared at a time. This register resets to $01.
Bits 0–3—Reserved
These bits are reserved and should be set to zero.
UN—Underrun
This bit indicates that the serial peripheral interface has encountered a transmitter underrun
condition while transmitting the associated data buffer. This error condition is only valid
when the serial peripheral interface is configured as a slave.
ME—Multimaster Error
This bit indicates that the SPISEL pin was asserted while the serial peripheral interface was
operating as a master. This indicates that there is a synchronization problem between
multiple masters on the SPI bus.
F—Full
Since the SPIRD register is the bottom of the receive FIFO, an empty SPIRD indicates the
receive FIFO is empty.
0 = The SPIRD register is empty.
1 = The SPIRD register has been filled with received data and indications about V, L,
and OV. The core is free to read the content of the receive data hold register. The
F bit should be cleared to enable the reception of another character.
E—Empty
Since the SPITD register is the top of the transmit FIFO, a full SPITD indicates that the
transmit FIFO is full.
0 = The SPITD register is full.
1 = The SPITD register is empty. The core is free to write to the transmit data hold
register. The E bit should be cleared to enable the transmission of another
character (writing to the SPITD register clears the E bit of the SPIER).
SPIER
BIT
0
1
2
3
4
5
6
7
FIELD
RESERVED
UN
ME
F
E