PIC18F2331 Datasheet, PDF (219/396 Pages) Microchip Technology – 28/40/44-Pin Enhanced Flash Microcontrollers with nanoWatt Technology, High Performance PWM and A/D

PIC18F2331/2431/4331/4431
18.3 SSP I²C Operation
The SSP module in I²C mode, fully implements all slave
functions, except general call support, and provides
interrupts on Start and Stop bits in hardware to facilitate
firmware implementations of the master functions. The
SSP module implements the standard mode
specifications, as well as 7-bit and 10-bit addressing.
Two pins are used for data transfer. These are the SCK/
SCL pin, which is the clock (SCL), and the SDI/SDA
pin, which is the data (SDA). The user must configure
these pins as inputs or outputs through the
TRISC<5:4> or TRISD<3:2> bits.
The SSP module functions are enabled by setting SSP
enable bit SSPEN (SSPCON<5>).
FIGURE 18-5:
SSP BLOCK DIAGRAM
(I²C MODE)
Read
Internal
Data Bus
Write
SCK/SCL⁽¹⁾
SDI/
SDA⁽¹⁾
SSPBUF reg
Shift
Clock
SSPSR reg
MSb
LSb
Match Detect
Addr Match
SSPADD reg
Start and
Stop bit Detect
Set, RESET
S, P bits
(SSPSTAT reg)
Note 1:
When SSPMX = 1 in CONFIG3H:
SCK/SCL is multiplexed to pin RC5,
SDA/SDI is multiplexed to pin RC4, and
SDO is multiplexed to pin RC7.
When SSPMX = 0 in CONFIG3H:
SCK/SCL is multiplexed to pin RD3,
SDA/SDI is multiplexed to pin RD2, and
SDO is multiplexed to pin RD1.
The SSP module has five registers for I²C operation.
These are the:
• SSP Control Register (SSPCON)
• SSP Status Register (SSPSTAT)
• Serial Receive/Transmit Buffer (SSPBUF)
• SSP Shift Register (SSPSR) – Not directly
accessible
• SSP Address Register (SSPADD)
The SSPCON register allows control of the I²C opera-
tion. Four mode selection bits (SSPCON<3:0>) allow
one of the following I²C modes to be selected:
• I²C Slave mode (7-bit address)
• I²C Slave mode (10-bit address)
• I²C Slave mode (7-bit address), with Start and
Stop bit interrupts enabled to support Firmware
Master mode
• I²C Slave mode (10-bit address), with Start and
Stop bit interrupts enabled to support Firmware
Master mode
• I²C Start and Stop bit interrupts enabled to sup-
port Firmware Master mode; Slave is Idle
Selection of any I²C mode with the SSPEN bit set,
forces the SCL and SDA pins to be open-drain,
provided these pins are programmed to inputs by
setting the appropriate TRISC or TRISD bits. Pull-up
resistors must be provided externally to the SCL and
SDA pins for proper operation of the I²C module.
Additional information on SSP I²C operation can be
found in the PICmicro^® Mid-Range MCU Family
Reference Manual (DS33023A).
18.3.1 SLAVE MODE
In Slave mode, the SCL and SDA pins must be config-
ured as inputs (TRISC<5:4> or TRISD<3:2> set). The
SSP module will override the input state with the output
data when required (slave-transmitter).
When an address is matched, or the data transfer after
an address match is received, the hardware automati-
cally will generate the Acknowledge (ACK) pulse, and
then load the SSPBUF register with the received value
currently in the SSPSR register.
There are certain conditions that will cause the SSP
module not to give this ACK pulse. They include (either
or both):
a) The buffer full bit BF (SSPSTAT<0>) was set
before the transfer was received.
b) The overflow bit SSPOV (SSPCON<6>) was set
before the transfer was received.
In this case, the SSPSR register value is not loaded
into the SSPBUF, but bit SSPIF (PIR1<3>) is set.
Table 18-2 shows what happens when a data transfer
byte is received, given the status of bits BF and
SSPOV. The shaded cells show the condition where
user software did not properly clear the overflow
condition. Flag bit BF is cleared by reading the
SSPBUF register, while bit SSPOV is cleared through
software.
The SCL clock input must have a minimum high and
low for proper operation. The high and low times of the
I²C specification, as well as the requirements of the
SSP module, are shown in timing parameter #100 and
parameter #101.
 2003 Microchip Technology Inc.
Preliminary
DS39616B-page 217