Datasheet
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MAX9257A/MAX9258A
Fully Programmable Serializer/Deserializer
with UART/I
2
C Control Channel
I
2
C
The MAX9257A features a UART-to-I
2
C converter that
converts UART packets to I
2
C. The UART-to-I
2
C con-
verter works as a repeater between the ECU and exter nal
I
2
C slave devices. The MAX9257A acts as the master
and converts UART read/write packets from the ECU to
I
2
C read/write for external I
2
C slave devices. For writes,
the UART-to-I
2
C converts the UART packets received
directly into I
2
C. For reads, the UART-to-I
2
C converter
follows the UART packet protocol. The I
2
C SCL clock
period is approximately the same as the UART bit clock
period (tUCLK). The I
2
C speed varies with UART speed.
I
2
C reads from the peripheral device do not disable the
ETO timer. Choose ETO large enough so that I
2
C read
commands are not lost due to ETO timing out.
I
2
C Timing
The MAX9257A acts like a master in I
2
C communication
with the peripheral device. The MAX9257A takes less
than 22 UART bit times to convert UART packets into I
2
C.
The SCL and SDA timings are based on the UART bit
clock. The I
2
C data rate is determined by UART and can
range from 95kbps to 4.25Mbps. The I
2
C timing require-
ments scale linearly from fast mode to higher speeds.
Table 31 shows the I
2
C timing information for data rates
greater than 400kbps. The I
2
C parameters scale with
t
UCLK
. See Figure 30 for timing parameters.
Table 31. Timing Information for I
2
C Data Rates Greater than 400kbps
Figure 30. I
2
C Timing Parameters
*t
UCLK
is equal to one UART period.
PARAMETER SYMBOL MIN TYP MAX UNIT
SCL Clock Frequency f
SCL
1 1 t
UCLK*
Start Condition Hold Time t
HD:STA
1 1 t
UCLK
Low Period of SCL Clock t
LOW
0.5 0.5 t
UCLK
High Period of SCL Clock t
HIGH
0.5 0.5 t
UCLK
Repeated START Condition Setup Time t
SU:STA
0.25 0.25 t
UCLK
Data Hold Time t
HD:DAT
0.25 0.25 t
UCLK
Data Setup Time t
SU:DAT
0.25 0.25 t
UCLK
Setup Time for STOP Condition t
SU:STO
0.25 0.25 t
UCLK
Bus Free Time t
BUF
0.5 0.5 t
UCLK
P
t
BUF
t
R
t
HD;STA
P
S
S
t
HD;STA
t
LOW
t
HD;DAT
t
HIGH
t
F
t
SU;DAT
t
SU;STA
t
SU;STO
SCL
SDA