MC908QY8CDWE Datasheet, PDF (176/232 Pages) Freescale Semiconductor, Inc – Addendum to MC68HC908QB8, rev. 3

Serial Peripheral Interface (SPI) Module
15.8.3 SPI Data Register
The SPI data register consists of the read-only receive data register and the write-only transmit data
register. Writing to the SPI data register writes data into the transmit data register. Reading the SPI data
register reads data from the receive data register. The transmit data and receive data registers are
separate registers that can contain different values. See Figure 15-2.
Bit 7
6
5
4
3
2
1
Bit 0
Read: R7
R6
R5
R4
R3
R2
R1
R0
Write: T7
T6
T5
T4
T3
T2
T1
T0
Reset:
Unaffected by reset
Figure 15-15. SPI Data Register (SPDR)
R7–R0/T7–T0 — Receive/Transmit Data Bits
NOTE
Do not use read-modify-write instructions on the SPI data register because
the register read is not the same as the register written.
MC68HC908QB8 Data Sheet, Rev. 3
174
Freescale Semiconductor