PIC16F87X
i) The MSSP module shifts in the ACK bit from the
slave device, and writes its value into the
SSPCON2 register ( SSPCON2<6>).
In I2C master mode, the BRG is reloaded automatically.
If Clock Arbitration is taking place for instance, the BRG
will be reloaded when the SCL pin is sampled high
(Figure 9-11).
j) The MSSP module generates an interrupt at the
end of the ninth clock cycle by setting the SSPIF
bit.
FIGURE 9-10: BAUD RATE GENERATOR
BLOCK DIAGRAM
k) The user generates a STOP condition by setting
the STOP enable bit PEN in SSPCON2.
SSPM3:SSPM0
SSPADD<6:0>
l) Interrupt is generated once the STOP condition
is complete.
9.2.8
BAUD RATE GENERATOR
SSPM3:SSPM0
SCL
Reload
Control
Reload
In I2C master mode, the reload value for the BRG is
located in the lower 7 bits of the SSPADD register
(Figure 9-10). When the BRG is loaded with this value,
the BRG counts down to 0 and stops until another
reload has taken place. The BRG count is decremented
twice per instruction cycle (TCY), on the Q2 and Q4
clock.
FOSC/4
BRG Down Counter
CLKOUT
FIGURE 9-11: BAUD RATE GENERATOR TIMING WITH CLOCK ARBITRATION
SDA
DX
DX-1
SCL allowed to transition high
SCL deasserted but slave holds
SCL low (clock arbitration)
SCL
BRG decrements
(on Q2 and Q4 cycles)
BRG
value
03h
02h
01h
00h (hold off)
03h
02h
SCL is sampled high, reload takes
place, and BRG starts its count.
BRG
reload
DS30292A-page 78
1999 Microchip Technology Inc.
MICROCHIP [ MICROCHIP ]
