Cirrus-logic EP93xx Manuel d'utilisateur télécharger pdf (Page 714)

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101

23-2 DS785UM1

Synchronous Serial Port

EP93xx User’s Guide

23.3 SSP Functionality

The SSP includes a programmable bit rate clock divider and prescaler to generate the serial

output clock SCLKOUT from the input clock SSPCLK. Bit rates are supported to 2MHz and

beyond, subject to choice of frequency for SSPCLK. The maximum bit rate will usually be

determined by peripheral devices.

The SSP operating mode, frame format and size are programmed though the control

registers SSPCR0, SSPCR1.

Three individually maskable interrupt outputs, SSPTXINTR, SSPRXINTR and SSPRORINTR

are generated:

• SSPTXINTR requests servicing of the transmit buffer

• SSPRXINTR requests servicing of the receive buffer

• SSPRORINTR indicates an overrun condition in the receive FIFO.

23.4 SSP Pin Multiplex

The SSP pins are multiplexed and may be used for the I

S controller instead of SSP by

setting DeviceCfg.I2SonSSP.

23.5 Configuring the SSP

Following reset, the SSP logic is disabled and must be configured when in this state. Control

registers SSPCR0 and SSPCR1 need to be programmed to configure the peripheral as a

master or slave operating under one of the following protocols:

• Motorola SPI

• Texas Instruments SSI

• National Semiconductor.

The bit rate, derived from the external SSPCLK, requires the programming of the clock

prescale register SSPCPSR. The following procedure must be used to initialize the SSP

function:

1. Set the enable bit (SSE) in register SSPCR1.

2. Write the other SSP configuration registers: SSPCR0 and SSPCPSR.

3. Clear the enable bit (SSE) in register SSPCR1.

4. Set the enable bit (SSE) in register SSPCR1.

23.5.1 Enabling SSP Operation

You can either prime the transmit FIFO, by writing up to eight 16-bit values when the SSP is

disabled, or allow the transmit FIFO service request to interrupt the CPU. Once enabled,

transmission or reception of data begins on the transmit (SSPTXD) and receive (SSPRXD)

pins.

1 2 ... 709 710 711 712 713 714 715 716 717 718 719 ... 823 824

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Cirrus-logic EP93xx Manuel d'utilisateur Page 714

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