HCS08 datasheet(205/290 Pages) MOTOROLA

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Data Sheet — MC9S08GB60/D V1.5

MOTOROLA

205

MC9S08GB/GT

SPTEF — SPI Transmit Buffer Empty Flag

This bit is set when there is room in the transmit data buffer. It is cleared by reading SPIS with SPTEF

set, followed by writing a data value to the transmit buffer at SPID. SPIS must be read with SPTEF = 1

before writing data to SPID or the SPID write will be ignored. SPTEF generates an SPTEF CPU

interrupt request if the SPTIE bit in the SPIC1 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 SPID 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 cleared

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 SS 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 (SPIC1).

1 = Mode fault error detected.

0 = No mode fault error.

12.4.5 SPI Data Register (SPID)

Figure 12-11 SPI Data Register (SPID)

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 SPID 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.

Bit 7

654321

Bit 0

Read:

Bit 7

654321

Bit 0

Write:

Reset:

00000000

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