The LOCK and ERROR outputs can be wired in an
AND configuration if you have multiple serializers and
deserializers, or a single serializer fanned out to multi-
ple deserializers through a repeater. For such situa-
tions, wire the multiple LOCK outputs together and use
a single pullup resistor to pull up all the lines high.
LOCK is high if all the devices are locked. Do the same
thing for ERROR; ERROR is low if any MAX9258 reports
errors.
Base Mode and Bypass Mode (Basics)
In the control channel phase, there are two modes: base
and bypass. In base mode, ECU always communicates
using the MAX9257/MAX9258 UART protocol and com-
munication with a peripheral device is performed in I
2
C
by the MAX9257. Packets not addressed to the
MAX9257 or the MAX9258 get converted to I
2
C and
passed to the peripheral device. Similarly, I
2
C packets
from the peripheral device get converted to UART pack-
ets in the reverse direction. ECU can disable communi-
cation to the peripheral device by writing a 0 to INTEN
(REG8[6] in the MAX9257 and REG7[6] in the MAX9258).
Base mode is the default mode. Bypass mode is entered
by writing a 0 to INTMODE and 1 to INTEN (Table 23).
Bypass mode is exited if there is no activity from ECU in
the control channel for the duration of CTO. When CTO
times out, INTEN reverts back to 0 and MAX9257/
MAX9258 revert back to base mode. To permanently
stay in bypass mode, ECU can lock the CTO timer or
program CTO to be longer than ETO and STO.
Timers
The MAX9257/MAX9258 feature three different timers.
The start timeout (STO) and end timeout (ETO) control
the duration of the control channel. The come-back
timeout (CTO) controls the duration of bypass mode.
STO Timer
The STO (start timeout) timer closes the control channel if
the ECU does not start using the control channel within
the STO timeout period. The STO timer is configured by
MAX9257/MAX9258
______________________________________________________________________________________ 27
Fully Programmable Serializer/Deserializer
with UART/I
2
C Control Channel
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