2010-2012 Microchip Technology Inc.
DS41440C-page 271
PIC16(L)F1825/1829
25.5.7
GENERAL CALL ADDRESS
SUPPORT
The addressing procedure for the I2C 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
I2C protocol, defined as address 0x00. When the
GCEN bit of the SSPxCON2 register is set, the slave
module will automatically ACK the reception of this
address regardless of the value stored in SSPxADD.
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
SSPxBUF
and
respond.
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 SSPxCON3 register is set, just
as with any other address reception, the slave
hardware will stretch the clock after the 8th falling
edge of SCLx. 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
25.5.8
SSPX MASK REGISTER
An SSPx Mask (SSPMSK) register (Register 25-5) is
available in I2C Slave mode as a mask for the value
held in the SSPxSR register during an address
comparison operation. A zero (‘0’) bit in the SSPMSK
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
SSPx operation until written with a mask value.
The SSPx 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 SSPx mask has no effect during the
reception of the first (high) byte of the address.
SDAx
SCLx
S
SSPxIF
BF (SSPxSTAT<0>)
Cleared by software
SSPxBUF is read
R/W = 0
ACK
General Call Address
Address is compared to General Call Address
Receiving Data
ACK
12
3
4
5
6
7
8
9
1
2
3
45
67
8
9
D7
D6
D5
D4
D3
D2
D1
D0
after ACK, set interrupt
GCEN (SSPxCON2<7>)
’1’
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