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Maxim Integrated Products 33
MAX9257A/MAX9258A
Fully Programmable Serializer/Deserializer
with UART/I2C Control Channel
sends three special synchronization words before enter-
ing the video phase. Training sequence is used to resyn-
chronize the devices before the video phase starts.
The MAX9257A/MAX9258A control channel duration is
independent of VSYNC. The control channel does not
close when VSYNC deasserts, which allows the use
of a VSYNC interrupt signal on VSYNC_IN. The control
channel must be closed by STO, ETO, or EF. If the con-
trol channel does not close before video data becomes
available, video data can be lost.
STO/ETO Timer Programming
STO and ETO can be programmed given the values of
T2, T4, and maximum values of T1, T3, and T5
(FigurestT = pixel clock period, tUCLK = UART period
When spread spectrum is not enabled in MAX9257A:
max(T1) = 2.5Fs + (3 x tT) + (4 x tUCLK)
When spread spectrum is enabled in MAX9257A:
max(T1) = 2.5Fs + (1400 x tT) + (4 x tUCLK)
T2 = tSTO
T4 = tETO
When pixel clock frequency range (PRATE) is 00 or 01:
STO
T
UCLK
ETO
T
UCLK
t
max(T3)
546
t
(20 t
)
8
t
max(T5)
546
t
(20 t
)
8
=
+
×
+
×
=
+
×
+
×
When pixel clock frequency range (PRATE) is 10 or 11:
STO
T
UCLK
ETO
T
UCLK
t
max(T3)
1090
t
(20 t
)
8
t
max(T5)
1090
t
(20 t
)
8
=
+
×
+
×
=
+
×
+
×
CTO Timer
The CTO (come-back timeout) timer temporarily or
permanently blocks programming to the MAX9257A/
MAX9258A registers. CTO keeps the devices in bypass
mode for the CTO timeout period
(Table 26). Bypass
mode can only be exited when the CTO timer expires.
The CTO timer uses the UART bit times for its counter.
Note that STO and ETO timers use the pixel clock while
CTO uses the UART bit times. The UART period tUCLK
synchronizes with the UART bit times, which synchronize
every time the SYNC frame is sent.
When the CTO timer times out, INTEN bit in both devices
is set to 0 and the devices revert back to base mode.
If communication with the MAX9257A/MAX9258A is not
needed after initial programming is complete, CTO may
be set to 000 (never come back). In this case, CTO never
expires and the devices stay in bypass mode until they
are powered down. This prevents accidental program-
ming of the devices while ECU communicates with the
peripheral using a different UART protocol from the
MAX9257A/MAX9258A UART protocol.
The overall CTO timeout is calculated as follows:
tCTO = tUCLK x CTO
Assuming a UART bit rate of 2Mbps, REG2[7:4],
REG3[7:4] = 100 (Table 26), CTO = 64, CTO timeout
calculated as:
tCTO = (0.5Fs) O 64 = 32Fs
Link Power-Up
The MAX9258A powers up when the power-down input
PD goes high. After approximately 130Fs, CCEN goes
high, indicating the control channel is available. This delay
is required because the analog circuitry has to fully wake
up. There are two ways to power up the MAX9257A. The
MAX9257A powers up according to the state of REM. ECU
powers up MAX9257A remotely (ECU sends command to
power up) when REM is pulled to VCC. The MAX9257A
powers up according to the supply voltage when REM is
grounded.
Table 26. CTO Counter Timeout Period
MAX9257A REG2[7:4]
MAX9258A REG3[7:4]
COUNTER USING UART BIT
TIMES
000
Never come back
(lockout)
001
16
010
32
011
48
100
64
101
80
110
96
111
112