PIC16F946 Datasheet, PDF (177/274 Pages) Microchip Technology – 64-Pin Flash-Based, 8-Bit CMOS Microcontrollers with LCD Driver and nanoWatt Technology

14.11 SSP I²C Operation
The SSP module in I²C mode, fully implements all
slave functions, except general call support, and pro-
vides interrupts on Start and Stop bits in hardware to
facilitate firmware implementations of the master func-
tions. 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
RC6/TX/CK/SCK/SCL/SEG9 pin, which is the clock
(SCL), and the RC7/RX/DT/SDI/SDA/SEG8 pin, which
is the data (SDA).
The SSP module functions are enabled by setting SSP
enable bit SSPEN (SSPCON<5>).
FIGURE 14-7:
SSP BLOCK DIAGRAM
(I²C™ MODE)
RC6/TX/
CK/SCK/
SCL/SEG9
RC7/
RX/DT/
SDI/
SDA/
SEG8
Read
Internal
Data Bus
Write
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)
The SSP module has five registers for the I²C operation,
which are listed below.
• SSP Control Register (SSPCON)
• SSP Status Register (SSPSTAT)
• Serial Receive/Transmit Buffer (SSPBUF)
• SSP Shift Register (SSPSR) – Not directly
accessible
• SSP Address Register (SSPADD)
PIC16F946
The SSPCON register allows control of the I²C
operation. 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
support 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, pro-
vided these pins are programmed to inputs by setting
the appropriate TRISC 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” (DS33023).
14.12 Slave Mode
In Slave mode, the SCL and SDA pins must be config-
ured as inputs (TRISC<7:6> 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 14-3
shows the results of 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. For high and low times of the I²C
specification, as well as the requirements of the SSP
module, see Section 19.0 “Electrical Specifications”.
© 2005 Microchip Technology Inc.
Preliminary
DS41265A-page 175