PIC18F2480_09 Datasheet, PDF (218/490 Pages) Microchip Technology – 28/40/44-Pin Enhanced Flash Microcontrollers with ECAN Technology, 10-Bit A/D and nanoWatt Technology

PIC18F2480/2580/4480/4580
18.4.7.1 Clock Arbitration
Clock arbitration occurs when the master, during any
receive, transmit or Repeated Start/Stop condition,
deasserts the SCL pin (SCL allowed to float high).
When the SCL pin is allowed to float high, the Baud
Rate Generator (BRG) is suspended from counting
until the SCL pin is actually sampled high. When the
SCL pin is sampled high, the Baud Rate Generator is
reloaded with the contents of SSPADD<6:0> and
begins counting. This ensures that the SCL high time
will always be at least one BRG rollover count in the
event that the clock is held low by an external device
(Figure 18-18).
FIGURE 18-18: BAUD RATE GENERATOR TIMING WITH CLOCK ARBITRATION
SDA
SCL
BRG
Value
BRG
Reload
DX
DX – 1
SCL deasserted but slave holds
SCL low (clock arbitration)
SCL allowed to transition high
BRG decrements on
Q2 and Q4 cycles
03h
02h
01h
00h (hold off)
03h
02h
SCL is sampled high, reload takes
place and BRG starts its count
DS39637D-page 218
© 2009 Microchip Technology Inc.