Datasheet

 2011-2013 Microchip Technology Inc. DS40001441D-page 233
PIC12(L)F1840
25.5.8 GENERAL CALL ADDRESS SUPPORT
The addressing procedure for the I
2
C bus is such that
the first byte after the Start condition usually
determines which device will be the slave addressed
by the master device. The exception is the general call
address which can address all devices. When this
address is used, all devices should, in theory, respond
with an acknowledge.
The general call address is a reserved address in the
I
2
C protocol, defined as address 0x00. When the
GCEN bit of the SSP1CON2 register is set, the slave
module will automatically ACK
the reception of this
address regardless of the value stored in SSP1ADD.
After the slave clocks in an address of all zeros with
the R/W
bit clear, an interrupt is generated and slave
software can read SSP1BUF and respond.
Figure 25-24 shows a General Call reception
sequence.
In 10-bit Address mode, the UA bit will not be set on
the reception of the general call address. The slave
will prepare to receive the second byte as data, just as
it would in 7-bit mode.
If the AHEN bit of the SSP1CON3 register is set, just
as with any other address reception, the slave
hardware will stretch the clock after the 8th falling
edge of SCL. The slave must then set its ACKDT
value and release the clock with communication
progressing as it would normally.
FIGURE 25-24: SLAVE MODE GENERAL CALL ADDRESS SEQUENCE
25.5.9 SSP1 MASK REGISTER
An SSP1 Mask (SSP1MSK) register (Register 25-5) is
available in I
2
C Slave mode as a mask for the value
held in the SSP1SR register during an address
comparison operation. A zero (‘0’) bit in the SSP1MSK
register has the effect of making the corresponding bit
of the received address a “don’t care.”
This register is reset to all ‘1’s upon any Reset
condition and, therefore, has no effect on standard
SSP1 operation until written with a mask value.
The SSP1 Mask register is active during:
• 7-bit Address mode: address compare of A<7:1>.
• 10-bit Address mode: address compare of A<7:0>
only. The SSP1 mask has no effect during the
reception of the first (high) byte of the address.
SDA
SCL
S
SSPIF
BF (SSPSTAT<0>)
Cleared by software
SSPBUF is read
R/W
= 0
ACK
General Call Address
Address is compared to General Call Address
Receiving Data
ACK
123456789123456789
D7 D6 D5 D4 D3 D2 D1 D0
after ACK
, set interrupt
GCEN (SSPCON2<7>)
’1’