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PIC18F2455/2550/4455/4550

19.0MASTER SYNCHRONOUS SERIAL PORT (MSSP) MODULE

19.1Master SSP (MSSP) Module Overview

The Master Synchronous Serial Port (MSSP) module is a serial interface, useful for communicating with other peripheral or microcontroller devices. These peripheral devices may be serial EEPROMs, shift registers, display drivers, A/D converters, etc. The MSSP module can operate in one of two modes:

Serial Peripheral Interface (SPI)

Inter-Integrated Circuit (I2C™)

-Full Master mode

-Slave mode (with general address call)

The I2C interface supports the following modes in hardware:

Master mode

Multi-Master mode

Slave mode

19.2Control Registers

The MSSP module has three associated control registers. These include a status register (SSPSTAT) and two control registers (SSPCON1 and SSPCON2). The use of these registers and their individual Configuration bits differ significantly depending on whether the MSSP module is operated in SPI or I2C mode.

Additional details are provided under the individual sections.

19.3SPI Mode

The SPI mode allows 8 bits of data to be synchronously transmitted and received simultaneously. All four modes of the SPI are supported. To accomplish communication, typically three pins are used:

Serial Data Out (SDO) – RC7/RX/DT/SDO

Serial Data In (SDI) – RB0/AN12/INT0/FLT0/SDI/SDA

Serial Clock (SCK) – RB1/AN10/INT1/SCK/SCL

Additionally, a fourth pin may be used when in a Slave mode of operation:

• Slave Select (SS) – RA5/AN4/SS/HLVDIN/C2OUT

Figure 19-1 shows the block diagram of the MSSP module when operating in SPI mode.

FIGURE 19-1: MSSP BLOCK DIAGRAM (SPI MODE)

Internal

Data Bus

Read Write

SSPBUF reg

SSPSR reg

SDI

bit0

 

Shift

 

 

 

Clock

SDO

 

 

 

 

 

SS Control

 

 

 

 

Enable

 

 

 

SS

Edge

 

 

 

 

Select

 

 

 

 

 

2

 

 

 

Clock Select

 

 

 

SSPM3:SSPM0

 

 

 

SMP:CKE 4

TMR2 Output

 

2

 

(

2

)

 

Edge

 

Select

Prescaler

TOSC

SCK

 

 

4, 16, 64

 

 

 

 

Data to TX/RX in SSPSR

TRIS bit

Note: Only those pin functions relevant to SPI operation are shown here.

2007 Microchip Technology Inc.

Preliminary

DS39632D-page 193

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