MC68HC08AZ0 Datasheet, PDF (251/444 Pages) Motorola, Inc – Advance Information

Freescale Semiconductor, Inc.
Serial Peripheral Interface Module (SPI)
I/O registers
The following formula is used to calculate the SPI baud rate:
Baud rate = ^{C-----G2-----M}_×-----BO----D-U-----T--
where:
CGMOUT = base clock output of the clock generator module (CGM)
BD = baud rate divisor
SPI data register
(SPDR)
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 2.
SPDR
Read:
Write:
Reset:
Bit 7
6
5
4
3
2
R7
R6
R5
R4
R3
R2
T7
T6
T5
T4
T3
T2
Indeterminate after reset
Figure 15. SPI data register (SPDR)
1
Bit 0
R1
R0
T1
T0
R7:R0/T7:T0 — Receive/Transmit data bits
NOTE: Read-modify-write instructions should not be used on the SPI data
register since the buffer read is not the same as the buffer written.
33-spi
MOTOROLA
Serial Peripheral Interface Module (SPI)
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MC68HC08AZ0
249