2002 Microchip Technology Inc.
Advance Information
DS41120B-page 99
PIC16C717/770/771
9.2.18
CONNECTION CONSIDERATIONS
FOR I2C BUS
For Standard mode I2C bus devices, the values of
resistors Rp and Rs in Figure 9-31 depends 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
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
. VDD as a function of Rp is shown in Figure 9-31.
The 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 9-31:
SAMPLE DEVICE CONFIGURATION FOR I2C BUS
TABLE 9-3:
REGISTERS ASSOCIATED WITH I2C OPERATION
Address
Name
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
POR, BOR
MCLR, WDT
0Bh, 8Bh,
10Bh,18Bh
INTCON
GIE
PEIE
T0IE
INTE
RBIE
T0IF
INTF
RBIF
0000 000x
0000 000u
0Ch
PIR1
ADIF
SSPIF
CCP1IF
TMR2IF
TMR1IF
-0-- 0000
8Ch
PIE1
ADIE
SSPIE
CCP1IE
TMR2IE
TMR1IE
-0-- 0000
0Dh
PIR2
LVDIF
BCLIF
CCP2IF
0--- 0--0
8Dh
PIE2
LVDIE
BCLIE
CCP2IE
0--- 0--0
13h
SSPBUF
Synchronous Serial Port Receive Buffer/Transmit Register
xxxx xxxx
uuuu uuuu
14h
SSPCON
WCOL
SSPOV
SSPEN
CKP
SSPM3
SSPM2
SSPM1
SSPM0
0000 0000
91h
SSPCON2
GCEN
ACKSTAT
ACKDT
ACKEN
RCEN
PEN
RSEN
SEN
0000 0000
94h
SSPSTAT
SMP
CKE
D/A
PS
R/W
UA
BF
0000 0000
93h
SSPADD
Synchronous Serial Port (I2C Mode) Address Register
0000 0000
Legend:
x
= unknown, u = unchanged, - = unimplemented read as '0'. Shaded cells are not used by the MSSP in I2C mode.
Rp
VDD + 10%
SDA
SCL
Note: I2C devices with input levels related to VDD must have one common supply line to which the pull-up resistor is also
DEVICE
Cb=10 pF to 400 pF
Rs
connected.
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