MC68HC908EY16 Datasheet, PDF (188/278 Pages) Motorola, Inc – Microcontrollers

Serial Peripheral Interface (SPI) Module
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 15-5. SPR1 and
SPR0 have no effect in slave mode. Reset clears SPR1 and SPR0.
Table 15-5. SPI Master Baud Rate Selection
SPR1:SPR0
00
01
10
11
Baud Rate Divisor (BD)
2
8
32
128
Use this formula to calculate the SPI baud rate:
Baud rate = ^{C-----2G-----M}_×----B-O----DU-----T--
where:
CGMOUT = base clock output of the internal clock generator module (ICG),
see Chapter 8 Internal Clock Generator (ICG) Module.
BD = baud rate divisor
15.13.3 SPI Data Register
The SPI data register is the read/write buffer for the receive data register and the 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
buffers that can contain different values. See Figure 15-2
Address: $000F
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 15-14. 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
buffer read is not the same as the buffer written.
MC68HC908EY16 • MC68HC908EY8 Data Sheet, Rev. 10
188
Freescale Semiconductor