Freescale Semiconductor MC68HC908MR32 manual SPI Data Register, SPI Master Baud Rate Selection

Serial Peripheral Interface Module (SPI)

Table 15-4. SPI Master Baud Rate Selection

SPR1:SPR0	Baud Rate Divisor (BD)
00	2
01	8
10	32
11	128

Use this formula to calculate the SPI baud rate:

CGMOUT Baud rate = --------------------------

2 ⋅ BD

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 Figure 15-2.

Address:	$0046
	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 15-16. 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.

MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1

214 Freescale Semiconductor