MC68HC908GR16 Datasheet, PDF (238/310 Pages) Motorola, Inc – Microcontrollers

Freescale Semiconductor, Inc.
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 16-4. SPR1 and SPR0 have no effect in slave mode. Reset clears SPR1
and SPR0.
Table 16-4. 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 = ^{C-----2G----M-}_×----B-O----DU-----T--
where:
CGMOUT = base clock output of the clock generator module (CGM)
BD = baud rate divisor
16.13.3 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 16-3.
NOTE:
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:
Unaffected by reset
Figure 16-16. SPI Data Register (SPDR)
R7–R0/T7–T0 — Receive/Transmit Data Bits
Do not use read-modify-write instructions on the SPI data register since the register
read is not the same as the register written.
Data Sheet
238
Serial Peripheral Interface (SPI) Module
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MC68HC908GR16 — Rev. 1.0
MOTOROLA