HC05V7GRSSLASHD datasheet(102/170 Pages) NXP

102 / 170 page

SECTION 14: SERIAL PERIPHERAL INTERFACE

Page 88

MC68HC05V7 Specification Rev. 1.0

CPOL - Clock Polarity

When the clock polarity bit is cleared and data is not being transferred, a steady

state low value is produced at the SCK pin of the master device. Conversely, if

this bit is set, the SCK pin will idle high. This bit is also used in conjunction with

the clock phase control bit to produce the desired clock-data relationship

between master and slave. Figure 14-1:

Data Clock Timing Diagram.

CPHA - Clock Phase

The clock phase bit, in conjunction with the CPOL bit, controls the clock-data

relationship between master and slave. The CPOL bit can be thought of as

simply inserting an inverter in series with the SCK line. The CPHA bit selects one

of two fundamentally different clocking protocols. When CPHA=0, the shift clock

is the OR of SCK with SS. As soon as SS goes low, the transaction begins and

the first edge on SCK invokes the first data sample. When CPHA=1, the SS pin

may be thought of as a simple output enable control. Figure 14-1:

Data Clock

Timing Diagram.

SPR1 and SPR0 - SPI Clock Rate Selects

These two bits select one of four baud rates (Figure 14-5) to be used as SCK if

the device is a master; however, they have no effect in the slave mode.

Figure 14-5:

Serial Peripheral Rate Selection

14.3.2

Serial Peripheral Status Register (SPSR)

Figure 14-6:

SPI Status Register (SPSR)

SPIF - SPI Transfer Complete Flag

The serial peripheral data transfer flag bit is set upon completion of data transfer

between the processor and external device. If SPIF goes high, and if SPIE is set,

a serial peripheral interrupt is generated. Clearing the SPIF bit is accomplished

by reading the SPSR (with SPIF set) followed by an access of the SPDR. Unless

SPSR is read (with SPIF set) first, attempts to write to SPDR are inhibited.

SPR1

SPR0

INT MCU CLOCK

DIVIDED BY

SPIF

—

MODF

————

WCOL

$0B

000000

RESET:

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

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