PIC16F87X Datasheet, PDF (96/218 Pages) Microchip Technology – 28/40-pin 8-Bit CMOS FLASH Microcontrollers

PIC16F87X
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 0.1VDD 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%
R_p
R_p
DEVICE
SDA
SCL
R_s
R_s
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.
DS30292C-page 94
 2001 Microchip Technology Inc.