Datasheet

DS28CM00: I²C/SMBus Silicon Serial Number
8 of 9
I²C Communication⎯Legend
SYMBOL DESCRIPTION SYMBOL DESCRIPTION
S START Condition A Acknowledged
AD,0 Select DS28CM00 for Write Access A\ Not Acknowledged
AD,1 Select DS28CM00 for Read Access <byte> Transfer of One Byte
Sr Repeated START Condition VMA Valid Memory Address (00h to 08h)
P STOP Condition IMA Invalid Memory Address
Command-Specific Communication⎯Color-Codes
Master-to-Slave Slave-to-Master
Communication Examples
Write to Control Register (address 08)
S AD,0 A 08h A <byte> A P
Write to ROM Address (excludes address 08)
S AD,0 A VMA A <byte> A\ P
Write to invalid address (>08)
S AD,0 A IMA A\ P
Read
S AD,0 A VMA A Sr AD,1 A <byte> A <byte> A\ P
Application Information
SDA and SCL Pullup Resistors
SDA is an open-drain output on the DS28CM00 that requires a pullup resistor (Figure 6) to realize high logic levels.
Because the DS28CM00 uses SCL only as input (no clock stretching) the master can drive SCL either through an
open-drain/collector output with a pullup resistor or a push-pull output.
Pullup Resistor R
P
Sizing
According to the I²C specification, a slave device must be able to sink at least 3mA at a V
OL
of 0.4V. The SMBus
specification requires a current sink capability of 4mA at 0.4V. The DS28CM00 can sink at least 4mA at 0.4V V
OL
over its entire operating voltage range. This DC characteristic determines the minimum value of the pullup resistor:
Rpmin = (V
CC
- 0.4V)/4mA. With a maximum operating voltage of 5.25V, the minimum value for the pullup resistor
is 1.2kΩ. The "Minimum RP" line in Figure 7 shows how the minimum pullup resistor changes with the operating
(pullup) voltage.
last byte
one or
more bytes
data is not accepted
address is not accepted
Set address pointer