MC68HC08AS32 Datasheet, PDF (225/280 Pages) Motorola, Inc – M68HC08 Family of 8-bit microcontroller units (MCUs)

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 14-5. SPR1 and SPR0 have no effect in slave mode. Reset clears SPR1
and SPR0.
Table 14-5. 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 clock generator module (CGM),
see Section 5. Clock Generator Module (CGM).
BD = baud rate divisor
14.13.3 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 14-2.
Address: $0012
Bit 7
6
Read: R7
R6
Write: T7
T6
Reset:
5
4
3
2
R5
R4
R3
R2
T5
T4
T3
T2
Unaffected by reset
1
Bit 0
R1
R0
T1
T0
Figure 14-16. SPI Data Register (SPDR)
NOTE:
R7–R0/T7–T0 — Receive/Transmit Data Bits
Do not use read-modify-write instructions on the SPI data register since the buffer
read is not the same as the buffer written.
MC68HC08AS32 — Rev. 4.1
Freescale Semiconductor
Data Sheet
225