M68HC05 datasheet(73/118 Pages) FREESCALE

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Functional Description

MC68HC05C9A Advance Information Data Sheet, Rev. 4.1

Freescale Semiconductor

the SPSR. In master mode the SS pin can be selected to be a general-purpose output (when configured

as an MC68HC05C9A) by writing a 1 in bit 5 of the port D data direction register, thus disabling the mode

fault circuit.

When CPHA = 0, the shift clock is the OR of SS with SCK. In this clock phase mode, SS must go high

between successive characters in an SPI message. When CPHA = 1, SS may be left low for several SPI

characters. In cases where there is only one SPI slave MCU, its SS line could be tied to VSS as long as

CPHA = 1 clock modes are used.

10.4 Functional Description

Figure 10-2 shows a block diagram of the serial peripheral interface circuitry. When a master device

transmits data to a slave via the MOSI line, the slave device responds by sending data to the master

device via the master’s MISO line. This implies full duplex transmission with both data out and data in

synchronized with the same clock signal. Thus, the byte transmitted is replaced by the byte received and

eliminates the need for separate transmit-empty and receive-full status bits. A single status bit (SPIF) is

used to signify that the I/O operation has been completed.

Figure 10-2. Serial Peripheral Interface Block Diagram

543210

SPE

SPIE

SPI CONTROL REGISTER (SPCR)

MSTR

CPOL

CPHA

SPR1

SPR2

$000A

WCOL

SPIF

SPI STATUS REGISTER (SPSR)

MODF

$000B

BIT 6

BIT 7

SPI DATA REGISTER (SPDR)

BIT 5

BIT 4

BIT 3

BIT 2

BIT 1

BIT 0

$000C

DWOM

SPI SHIFT REGISTER

DIVIDER

CLOCK

LOGIC

SPDR ($000C)

7 6 5 4 3 2 1 0

MODF

WCOL

SPIF

SPR1

SPR0

CPOL

CPHA

MSTR

SPE

SPIE

PD3/

MOSI

PD2/

MISO

÷ 2

÷ 32

÷ 16

÷ 4

SELECT

SPI

CONTROL

INTERNAL DATA BUS

MSTR

INTERNAL

CLOCK

(XTAL

÷2)

SPI CLOCK (MASTER)

SPI INTERRUPT REQUEST

PD4/

SCK

PD5/

(SLAVE)

SPI

(MASTER)

CLOCK

M68HC05 Datasheet(PDF) 73 Page - Freescale Semiconductor, Inc

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