Datasheet
2005-2015 Microchip Technology Inc. DS40001262F-page 175
PIC16F631/677/685/687/689/690
13.0 SSP MODULE OVERVIEW
The Synchronous Serial Port (SSP) module is a serial
interface used to communicate with other peripheral or
microcontroller devices. These peripheral devices
may be serial EEPROMs, shift registers, display
drivers, A/D converters, etc. The SSP module can
operate in one of two modes:
• Serial Peripheral Interface (SPI)
• Inter-Integrated Circuit (I
2
C™)
Refer to Application Note AN578, “Use of the SSP
Module in the Multi-Master Environment” (DS00578).
13.1 SPI Mode
This section contains register definitions and operational
characteristics of the SPI module.
The SPI mode allows eight bits of data to be
synchronously transmitted and received simultaneously.
To accomplish communication, typically three pins are
used:
• Serial Data Out (SDO)
• Serial Data In (SDI)
• Serial Clock (SCK)
Additionally, a fourth pin may be used when in a Slave
mode of operation:
• Slave Select (SS
)
FIGURE 13-1: SSP BLOCK DIAGRAM
(SPI MODE)
Note 1: When the SPI is in Slave mode with SS
pin control enabled (SSPM<3:0> bits of
the SSPCON register = 0100), the SPI
module will reset if the SS
pin is set to
V
DD.
2: If the SPI is used in Slave mode with
CKE = 1, then the SS
pin control must be
enabled.
3: When the SPI is in Slave mode with SS
pin control enabled (SSPM<3:0> bits of
the SSPCON register = 0100), the state
of the SS
pin can affect the state read
back from the TRISC<4> bit. The
peripheral OE signal from the SSP
module into PORTC controls the state
that is read back from the TRISC<4> bit
(see Section 17.0 “Electrical
Specifications” for information on
PORTC). If read-write-modify
instructions, such as BSF, are performed
on the TRISC register while the SS
pin is
high, this will cause the TRISC<7> bit to
be set, thus disabling the SDO output.
Read Write
Internal
Data Bus
SCK/
SSPSR Reg
SSPBUF Reg
SSPM<3:0>
bit 0
Shift
Clock
SS
Control
Enable
Edge
Select
Clock Select
TMR2 Output
T
CY
Prescaler
4, 16, 64
TRISB<6>
2
Edge
Select
2
4
SCL
Peripheral OE
SDI/SDA
SDO
SS