PIC16F872_06 Datasheet, PDF (80/168 Pages) Microchip Technology – 28-Pin, 8-Bit CMOS Flash Microcontroller with 10-Bit A/D

PIC16F872
9.3 Connection Considerations for I²C
Bus
For standard mode I²C bus devices, the values of
resistors R_p and R_s in Figure 9-27 depend on the fol-
lowing parameters:
• Supply voltage
• Bus capacitance
• Number of connected devices
(input current + leakage current).
The supply voltage limits the minimum value of resistor
R_p, due to the specified minimum sink current of 3 mA
at VOL max = 0.4V, for the specified output stages. For
example, with a supply voltage of VDD = 5V+10% and
VOL max = 0.4V at 3 mA, R_{p min} = (5.5-0.4)/0.003 =
1.7 kΩ. VDD, as a function of R_p, is shown in
Figure 9-27. The desired noise margin of 0.1 VDD for
the low level limits the maximum value of R_s. Series
resistors are optional and used to improve ESD
susceptibility.
The bus capacitance is the total capacitance of wire,
connections, and pins. This capacitance limits the max-
imum value of R_p, due to the specified rise time
(Figure 9-27).
The SMP bit is the slew rate control enabled bit. This bit
is in the SSPSTAT register, and controls the slew rate
of the I/O pins when in I²C mode (master or slave).
FIGURE 9-27:
SAMPLE DEVICE CONFIGURATION FOR I²C BUS
VDD + 10%
Rp
Rp
DEVICE
Rs Rs
SDA
SCL
C_b=10 - 400 pF
Note: I²C devices with input levels related to VDD must have one common supply line to which the pull-up resistor is
also connected.
DS30221C-page 78
© 2006 Microchip Technology Inc.