PIC16F87XA
FIGURE 9-1:
MSSP BLOCK DIAGRAM
(SPI MODE)
9.0
9.1
MASTER SYNCHRONOUS
SERIAL PORT (MSSP)
MODULE
Internal
Data Bus
Read
Write
Master SSP (MSSP) Module
Overview
SSPBUF reg
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, dis-
play drivers, A/D converters, etc. The MSSP module
can operate in one of two modes:
RC4/
SDI/
SDA
SSPSR reg
Shift
Clock
bit0
RC5/SDO
• Serial Peripheral Interface (SPI)
• Inter-Integrated Circuit (I2C)
- Full Master Mode
Peripheral OE
RA5/
SS/
AN4
Control
Enable
SS
- Slave mode (with general address call)
The I2C interface supports the following modes in
hardware:
Edge
Select
• Master mode
• Multi-Master mode
• Slave mode
2
Clock Select
RC3/
SCK/
SCL/
LVDIN
SSPM3:SSPM0
9.2
Control Registers
SMP:CKE
2
4
TMR2 output
2
(
)
The MSSP module has three associated registers.
These include a status register (SSPSTAT) and two
control registers (SSPCON and SSPCON2). The uses
of these registers and their individual configuration bits
differ significantly, depending on whether the MSSP
module is operated in SPI or I2C mode.
Edge
Select
TOSC
Prescaler
4, 16, 64
Data to TX/RX in SSPSR
TRIS bit
Additional details are provided under the individual
sections.
Note: When the SPI is in Slave mode with SS pin
control enabled (SSPCON<3:0> = 0100),
the state of the SS pin can affect the state
read back from the TRISC<5> bit. The
Peripheral OE signal from the SSP module
into PORTC, controls the state that is read
back from the TRISC<5> bit (see
Section 4.3 for information on PORTC). If
Read-Modify-Write instructions, such as
BSF,are performed on the TRISC register
while the SS pin is high, this will cause the
TRISC<5> bit to be set, thus disabling the
SDO output.
9.3
SPI Mode
The SPI mode allows 8 bits of data to be synchronously
transmitted and received simultaneously. All four
modes of SPI are supported. To accomplish communi-
cation, typically three pins are used:
• Serial Data Out (SDO) - RC5/SDO
• Serial Data In (SDI) - RC4/SDI/SDA
• Serial Clock (SCK) - RC3/SCK/SCL/LVDIN
Additionally a fourth pin may be used when in a Slave
mode of operation:
• Slave Select (SS) - RA5/SS/AN4
Figure 9-1 shows the block diagram of the MSSP
module when operating in SPI mode.
2001 Microchip Technology Inc.
Advance Information
DS39582A-page 69
MICROCHIP [ MICROCHIP ]
