MC68HC908GR8 Datasheet, PDF (224/286 Pages) Freescale Semiconductor, Inc – M68HC08 Microcontrollers

Serial Peripheral Interface (SPI)
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 20-4. SPR1 and
SPR0 have no effect in slave mode. Reset clears SPR1 and SPR0.
Table 20-4. SPI Master Baud Rate Selection
SPR1 and SPR0
00
01
10
11
Baud Rate Divisor (BD)
2
8
32
128
Use this formula to calculate the SPI baud rate:
Baud rate = ^BUSCLK
BD
where:
BD = baud rate divisor
20.13.3 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 20-2.
Address: $0012
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:
Indeterminate after reset
Figure 20-15. 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 since the
register read is not the same as the register written.
MC68HC908GR8 • MC68HC908GR4 Data Sheet, Rev. 7
224
Freescale Semiconductor