MC9S08RG60 Datasheet, PDF (175/232 Pages) Motorola, Inc – Microcontrollers

SoC Guide — MC9S08RG60/D Rev 1.10
SPTEF — SPI Transmit Buffer Empty Flag
This bit is set when there is room in the transmit data buffer. It is cleared by reading SPI1S with SPTEF
set, followed by writing a data value to the transmit buffer at SPI1D. SPI1S must be read with
SPTEF = 1 before writing data to SPI1D or the SPI1D write will be ignored. SPTEF generates an
SPTEF CPU interrupt request if the SPTIE bit in the SPI1C1 is also set. SPTEF is automatically set
when a data byte transfers from the transmit buffer into the transmit shift register. For an idle SPI (no
data in the transmit buffer or the shift register and no transfer in progress), data written to SPI1D is
transferred to the shifter almost immediately so SPTEF is set within two bus cycles allowing a second
8-bit data value to be queued into the transmit buffer. After completion of the transfer of the value in
the shift register, the queued value from the transmit buffer will automatically move to the shifter and
SPTEF will be set to indicate there is room for new data in the transmit buffer. If no new data is waiting
in the transmit buffer, SPTEF simply remains set and no data moves from the buffer to the shifter.
1 = SPI transmit buffer empty.
0 = SPI transmit buffer not empty.
MODF — Master Mode Fault Flag
MODF is set if the SPI is configured as a master and the slave select input goes low, indicating some
other SPI device is also configured as a master. The SS1 pin acts as a mode fault error input only when
MSTR = 1, MODFEN = 1, and SSOE = 0; otherwise, MODF will never be set. MODF is cleared by
reading MODF while it is 1, then writing to SPI control register 1 (SPI1C1).
1 = Mode fault error detected.
0 = No mode fault error.
12.4.5 SPI Data Register (SPI1D)
Bit 7
6
5
4
3
2
Read:
Bit 7
6
5
4
3
2
Write:
Reset: 0
0
0
0
0
0
Figure 12-11 SPI Data Register (SPI1D)
1
Bit 0
1
Bit 0
0
0
Reads of this register return the data read from the receive data buffer. Writes to this register write data
to the transmit data buffer. When the SPI is configured as a master, writing data to the transmit data
buffer initiates an SPI transfer.
Data should not be written to the transmit data buffer unless the SPI transmit buffer empty flag
(SPTEF) is set, indicating there is room in the transmit buffer to queue a new transmit byte.
Data may be read from SPI1D any time after SPRF is set and before another transfer is finished. Failure
to read the data out of the receive data buffer before a new transfer ends causes a receive overrun
condition and the data from the new transfer is lost.
Freescale Semiconductor
MC9S08RC/RD/RE/RG
175