Datasheet

I/O Registers
MC68HC908GP32 Data Sheet, Rev. 10
Freescale Semiconductor 193
SPR1 and SPR0 — SPI Baud Rate Select Bits
In master mode, these read/write bits select one of four baud rates as shown in Table 15-4. SPR1 and
SPR0 have no effect in slave mode. Reset clears SPR1 and SPR0.
Use this formula to calculate the SPI baud rate:
15.13.3 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.)
R7–R0/T7–T0 — Receive/Transmit Data Bits
NOTE
Do not use read-modify-write instructions on the SPI data register since the
register read is not the same as the register written.
Table 15-4. SPI Master Baud Rate Selection
SPR1 and SPR0 Baud Rate Divisor (BD)
00 2
01 8
10 32
11 128
Address: $0012
Bit 7654321Bit 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)
Baud rate
BUSCLK
2 BD×
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