MAX6618
Packet Error Checksum (PEC)
All MAX6618 I
2
C packets have an optional packet error
checksum (PEC). The PEC is implemented in accor-
dance with the SMBus specification, versions 1.1 and
2. The MAX6618 accepts commands with or without
PEC. The PEC for device responses is optional and can
be disabled in the CONFIG0 register.
Applications Information
Operation with Multiple Masters
If the MAX6618 is operated on a 2-wire interface with
multiple masters, a master reading the MAX6618
should use a repeated START between the write that
sets the MAX6618’s address pointer, and the read(s)
that takes the data from the location(s) (Table 16). This
is because it is possible for master 2 to take over the
bus after master 1 has set up the MAX6618’s address
pointer, but before master 1 has read the data. If mas-
ter 2 subsequently changes the MAX6618’s address
pointer, master 1’s delayed read can be from an unex-
pected location. The use of multiple masters is not rec-
ommended.
I
2
C Address Range
In addition to the four MSBs (0101), the I
2
C slave
address includes bit A0 (set by the address input AD0)
and bits A2:A1 (set to 01). See Table 16.
Choosing Pullup Resistors
I
2
C requires pullup resistors to provide a logic-high level
to data and clock lines. There are tradeoffs between
power dissipation and speed, and a compromise must
be made in choosing pullup resistor values. Every device
connected to the bus introduces some capacitance even
when the device is not in operation. I
2
C specifies a mini-
mum 300ns rise time to go from low to high (30% to 70%)
for fast mode, which is defined for a date rate of 400kbps
(refer to the I
2
C specifications for details). To meet the
rise time requirement, choose pullup resistors so that the
rise time t
R
= 0.85R
PULLUP
x C
BUS
< 300ns. For typical
low bus capacitances, a 4.7kΩ resistor can be used. For
a bus capacitance of 400pF, choose a pullup resistor
less than 880Ω. Many I
2
C devices work when the mini-
mum specified rise time is not met. However, if the time it
takes for the waveform to rise becomes too slow, these
waveforms are not recognized by the master.
PECI-to-I
2
C Translator
16 ______________________________________________________________________________________
