Freescale Semiconductor MCF51QE128RM manual SPI Baud Rate Generation, Freescale Semiconductor 319

Models: MCF51QE128RM

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Pin Control

 

 

 

 

 

 

 

M

MOSI

SPE

 

 

 

 

 

S

 

 

 

 

 

(MOMI)

 

 

 

 

 

 

 

 

Tx Buffer (Write SPIxD)

 

 

 

 

Enable

 

 

 

 

 

M

 

SPI System

 

 

 

 

MISO

 

 

 

 

 

 

Shift

SPI Shift Register

Shift

 

S

(SISO)

 

 

 

 

Out

In

 

 

 

 

 

 

 

 

 

 

 

Rx Buffer (Read SPIxD)

 

SPC0

 

 

 

 

 

 

 

 

 

 

 

 

 

BIDIRO

 

 

LSBFE

Shift

Shift

Rx Buffer

Tx Buffer

 

 

 

Direction

Clock

Full

Empty

 

 

 

 

 

 

 

 

 

 

 

 

Master Clock

M

 

Bus Rate

SPIxBR

Clock

 

 

 

 

 

 

 

 

SPSCK

Clock

Clock Generator

Logic

 

 

Slave Clock

S

 

 

 

 

 

 

 

 

 

MSTR

Master/Slave

 

 

 

 

Master/

 

Mode Select

 

 

 

 

Slave

 

 

 

 

 

 

 

 

 

 

 

 

MODFEN

 

 

 

 

Mode Fault

 

 

SSOE

 

SS

 

 

 

 

 

 

 

 

Detection

 

 

 

 

 

 

 

 

 

 

 

 

 

 

SPRF

SPTEF

 

 

 

 

 

 

 

 

 

 

 

 

 

 

SPTIE

 

 

 

 

 

 

 

 

 

SPI

 

MODF

SPIE

Interrupt Request

Figure 16-3. SPI Module Block Diagram

16.1.5SPI Baud Rate Generation

As shown in Figure 16-4, the clock source for the SPI baud rate generator is the bus clock. The three prescale bits (SPIxBR[SPPR]) choose a prescale divisor of 1, 2, 3, 4, 5, 6, 7, or 8. The three rate select bits (SPIxBR[SPR]) divide the output of the prescaler stage by 2, 4, 8, 16, 32, 64, 128, or 256 to obtain the internal SPI master mode bit-rate clock.

MCF51QE128 MCU Series Reference Manual, Rev. 3

Freescale Semiconductor

319

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Freescale Semiconductor MCF51QE128RM manual SPI Baud Rate Generation, Freescale Semiconductor 319