Spi Data Register - Freescale Semiconductor MC68HC908MR16 Datasheet

Serial Peripheral Interface Module (SPI)
Use this formula to calculate the SPI baud rate:
where:
CGMOUT = base clock output of the clock generator module (CGM)
BD = baud rate divisor

15.12.3 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
Address: $0046
Read:
Write:
Reset:
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.
214
Table 15-4. SPI Master Baud Rate Selection
SPR1:SPR0
00
01
10
11
Baud rate
Bit 7 6 5
R7 R6 R5
T7 T6 T5
Figure 15-16. SPI Data Register (SPDR)
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1
Baud Rate Divisor (BD)
2
8
32
128
CGMOUT
= ------------------------- -
×
2 BD
Figure 15-2.
4 3 2
R4 R3 R2
T4 T3 T2
Indeterminate after reset
NOTE
1 Bit 0
R1 R0
T1 T0
Freescale Semiconductor