Vault 7: Projects
This publication series is about specific projects related to the Vault 7 main publication.
2007-2014 Microchip Technology Inc. DS70000195F-page 61
Inter-Integrated Circuit™ (I
2
C™)
8.0 CONNECTION CONSIDERATIONS FOR I
2
C BUS
Because the I
2
C bus is a wired-AND bus connection, pull-up resistors (RP) on the bus are
required, as illustrated in Figure 8-1. The series resistors (R
S) are optional and are used to
improve the Electrostatic Discharge (ESD) susceptibility.
The values of the resistors, R
P and RS, depend on the following parameters:
• Supply voltage
• Bus capacitance
• Number of connected devices (input current + leakage current)
• Input level selection (I
2
C or System Management Bus (SMBus))
Because the device must be able to pull the bus low against R
P, current drawn by RP must be
greater than the I/O pin minimum sink current, I
OL at VOLMAX, for the device output stage.
Equation 8-1 shows the formula for computing the minimum pull-up resistance.
Equation 8-1: Minimum Pull-up Resistance
In a 400 kHz system, a minimum rise time specification of 300 ns exists; in a 100 kHz system,
the specification is 1000 ns. Because RP must pull the bus up against the total capacitance, CB,
with a maximum rise time of 300 ns to (V
DD – 0.7V), the maximum resistance for the pull-up
(R
PMAX) is computed using the formula as shown in Equation 8-2.
Equation 8-2: Maximum Pull-up Resistance
The maximum value for R
S is determined by the desired noise margin for the low level. RS cannot
drop enough voltage to make the device V
OL and the voltage across RS more than the maximum
V
IL. Equation 8-3 shows the formula for computing the maximum value for RS.
Equation 8-3: Maximum Series Resistance
Note: The SCLx clock input must have a minimum high and low time for proper operation.
Refer to the “Electrical Characteristics” chapter in the specific device data sheet
for more information on the high and low times of the I
2
C bus specification, and
requirements of the I
2
C module and I/O pins.
RPMIN =
(VDDMAX – VOLMAX)
I
OL
– tR
C
B * [ln(1 – (VDDMAX – VILMAX))]
RSMAX =
(V
ILMAX – VOLMAX)
I
OLMAX
Protego_Release_01_05-Related-OEM-Documentation-PIC24FJ32MC10X-Reference_Manual-PIC24FJ32MC102-I2C.pdf