Freescale Semiconductor MC68HC908MR32 Manual Do Utilizador
Serial Peripheral Interface Module (SPI)
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1
214
Freescale Semiconductor
Use this formula to calculate the SPI baud rate:
where:
CGMOUT = base clock output of the clock generator module (CGM)
BD = baud rate divisor
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
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
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.
register read is not the same as the register written.
Table 15-4. SPI Master Baud Rate Selection
SPR1:SPR0
Baud Rate Divisor (BD)
00
2
01
8
10
32
11
128
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)
Baud rate
CGMOUT
2
BD
×
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