
PIC16F87X
DS30292C-page 94
2001 Microchip Technology Inc.
9.3
Connection Considerations for
I2C Bus
For standard-mode I2C bus devices, the values of
lowing parameters:
Supply voltage
Bus capacitance
Number of connected devices
(input current + leakage current)
The supply voltage limits the minimum value of resistor
Rp, 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, Rp min = (5.5-0.4)/0.003 = 1.7 k.
desired noise margin of 0.1VDD for the low level limits
the maximum value of Rs. 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 Rp due to the specified rise time
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
Rp
VDD + 10%
SDA
SCL
DEVICE
Cb=10 - 400 pF
Rs
Note: I2C devices with input levels related to VDD must have one common supply line to which the pull-up resistor is also
connected.