Datasheet

© 2009 Microchip Technology Inc. DS39682E-page 159
PIC18F45J10 FAMILY
16.4 I
2
C Mode
The MSSP module in I
2
C mode fully implements all
master and slave functions (including general call
support) and provides interrupts on Start and Stop bits
in hardware to determine a free bus (multi-master
function). The MSSP module implements the standard
mode specifications, as well as 7-bit and 10-bit
addressing.
Two pins are used for data transfer:
• Serial clock (SCLx) – RC3/SCK1/SCL1 or
RD6/SCK2/SCL2
• Serial data (SDAx) – RC4/SDI1/SDA1 or
RD5/SDI2/SDA2
The user must configure these pins as inputs by setting
the associated TRIS bits.
FIGURE 16-7: MSSP BLOCK DIAGRAM
(I
2
C™ MODE)
16.4.1 REGISTERS
The MSSP module has six registers for I
2
C operation.
These are:
• MSSP Control Register 1 (SSPxCON1)
• MSSP Control Register 2 (SSPxCON2)
• MSSP Status Register (SSPxSTAT)
• Serial Receive/Transmit Buffer Register
(SSPxBUF)
• MSSP Shift Register (SSPxSR) – Not directly
accessible
• MSSP Address Register (SSPxADD)
SSPxCON1, SSPxCON2 and SSPxSTAT are the
control and status registers in I
2
C mode operation. The
SSPxCON1 and SSPxCON2 registers are readable
and writable. The lower 6 bits of the SSPxSTAT are
read-only. The upper two bits of the SSPxSTAT are
read/write.
Many of the bits in SSPxCON2 assume different
functions, depending on whether the module is operat-
ing in Master or Slave mode; bits<5:2> also assume
different names in Slave mode. The different aspects of
SSPxCON2 are shown in Register 16-5 (for Master
mode) and Register 16-6 (Slave mode).
SSPxSR is the shift register used for shifting data in or
out. SSPxBUF is the buffer register to which data bytes
are written to or read from.
SSPxADD register holds the slave device address
when the MSSP is configured in I
2
C Slave mode. When
the MSSP is configured in Master mode, the lower
seven bits of SSPxADD act as the Baud Rate
Generator reload value.
In receive operations, SSPxSR and SSPxBUF together
create a double-buffered receiver. When SSPxSR
receives a complete byte, it is transferred to SSPxBUF
and the SSPxIF interrupt is set.
During transmission, the SSPxBUF is not
double-buffered. A write to SSPxBUF will write to both
SSPxBUF and SSPxSR.
Read Write
SSPxSR reg
Match Detect
SSPxADD reg
SSPxBUF reg
Internal
Data Bus
Addr Match
Set, Reset
S, P bits
(SSPxSTAT reg)
Shift
Clock
MSb
LSb
Note: Only port I/O names are used in this diagram for
the sake of brevity. Refer to the text for a full list of
multiplexed functions.
SCLx
SDAx
Start and
Stop bit Detect
Address Mask
Note: Disabling the MSSP module by clearing
the SSPEN (SSPxCON1<5>) bit may not
reset the module. It is recommended to
clear the SSPxSTAT, SSPxCON1 and
SSPxCON2 registers and select the mode
prior to setting the SSPEN bit to enable
the MSSP module.