Datasheet

© 2006 Microchip Technology Inc. DS70117F-page 97
dsPIC30F6011/6012/6013/6014
15.2 I
2
C Module Addresses
The I2CADD register contains the Slave mode
addresses. The register is a 10-bit register.
If the A10M bit (I2CCON<10>) is ‘0’, the address is
interpreted by the module as a 7-bit address. When an
address is received, it is compared to the 7 LSbs of the
I2CADD register.
If the A10M bit is ‘1’, the address is assumed to be a
10-bit address. When an address is received, it will be
compared with the binary value ‘11110 A9 A8’ (where
A9 and A8 are two Most Significant bits of I2CADD). If
that value matches, the next address will be compared
with the Least Significant 8 bits of I2CADD, as specified
in the 10-bit addressing protocol.
15.3 I
2
C 7-bit Slave Mode Operation
Once enabled (I2CEN = 1), the slave module will wait
for a Start bit to occur (i.e., the I
2
C module is ‘Idle’). Fol-
lowing the detection of a Start bit, 8 bits are shifted into
I2CRSR and the address is compared against
I2CADD. In 7-bit mode (A10M = 0), bits I2CADD<6:0>
are compared against I2CRSR<7:1> and I2CRSR<0>
is the R_W bit. All incoming bits are sampled on the
rising edge of SCL.
If an address match occurs, an Acknowledgement will
be sent, and the slave event interrupt flag (SI2CIF) is
set on the falling edge of the ninth (ACK
) bit. The
address match does not affect the contents of the
I2CRCV buffer or the RBF bit.
15.3.1 SLAVE TRANSMISSION
If the R_W bit received is a ‘1’, then the serial port will
go into Transmit mode. It will send ACK
on the ninth bit
and then hold SCL to ‘0’ until the CPU responds by writ-
ing to I2CTRN. SCL is released by setting the SCLREL
bit, and 8 bits of data are shifted out. Data bits are
shifted out on the falling edge of SCL, such that SDA is
valid during SCL high. The interrupt pulse is sent on the
falling edge of the ninth clock pulse, regardless of the
status of the ACK
received from the master.
15.3.2 SLAVE RECEPTION
If the R_W bit received is a ‘0’ during an address
match, then Receive mode is initiated. Incoming bits
are sampled on the rising edge of SCL. After 8 bits are
received, if I2CRCV is not full or I2COV is not set,
I2CRSR is transferred to I2CRCV. ACK
is sent on the
ninth clock.
If the RBF flag is set, indicating that I2CRCV is still
holding data from a previous operation (RBF = 1), then
ACK
is not sent; however, the interrupt pulse is gener-
ated. In the case of an overflow, the contents of the
I2CRSR are not loaded into the I2CRCV.
15.4 I
2
C 10-bit Slave Mode Operation
In 10-bit mode, the basic receive and transmit opera-
tions are the same as in the 7-bit mode. However, the
criteria for address match is more complex.
The I
2
C specification dictates that a slave must be
addressed for a write operation with two address bytes
following a Start bit.
The A10M bit is a control bit that signifies that the
address in I2CADD is a 10-bit address rather than a 7-bit
address. The address detection protocol for the first byte
of a message address is identical for 7-bit and 10-bit
messages, but the bits being compared are different.
I2CADD holds the entire 10-bit address. Upon receiv-
ing an address following a Start bit, I2CRSR <7:3> is
compared against a literal ‘11110’ (the default 10-bit
address) and I2CRSR<2:1> are compared against
I2CADD<9:8>. If a match occurs and if R_W = 0, the
interrupt pulse is sent. The ADD10 bit will be cleared to
indicate a partial address match. If a match fails or
R_W = 1, the ADD10 bit is cleared and the module
returns to the Idle state.
The low byte of the address is then received and com-
pared with I2CADD<7:0>. If an address match occurs,
the interrupt pulse is generated and the ADD10 bit is
set, indicating a complete 10-bit address match. If an
address match did not occur, the ADD10 bit is cleared
and the module returns to the Idle state.
15.4.1 10-BIT MODE SLAVE
TRANSMISSION
Once a slave is addressed in this fashion with the full
10-bit address (we will refer to this state as
“PRIOR_ADDR_MATCH”), the master can begin
sending data bytes for a slave reception operation.
TABLE 15-1: 7-BIT I
2
C™ SLAVE
ADDRESSES SUPPORTED
BY DSPIC30F
0x00 General call address or Start byte
0x01-0x03 Reserved
0x04-0x07 Hs mode Master codes
0x08-0x77 Valid 7-bit addresses
0x78-0x7b Valid 10-bit addresses (lower 7
bits)
0x7c-0x7f Reserved
Note: The I2CRCV will be loaded if the I2COV
bit = 1 and the RBF flag = 0. In this case,
a read of the I2CRCV was performed but
the user did not clear the state of the
I2COV bit before the next receive
occurred. The Acknowledgement is not
sent (ACK
= 1) and the I2CRCV is
updated.