Rainbow Electronics MAX9258 - Manual (Page 28)

MAX9257/MAX9258
register REG2 for both the MAX9257 and the MAX9258.
The four bits of REG2[7:4] select the divide ratio (STODIV)
for the STO clock as a function of the pixel clock (Table
24). The timeout period is determined by counter bits
REG2[3:0] that increment once every STO clock period.
Write to REG2[3:0] to determine the counter end time.
The STO counter counts to the programmed STOCNT +
1. The ECU must begin communicating before STO times
out, otherwise, the control channel closes (Figure 22). The
STO timeout period is given by:
For example:
If the pixel clock frequency is set to 16MHz, STODIV is
set to 1010 (STODIV = 1024), and STOCNT is set to
1001 (STOCNT = 9), the STO timer counts with
15.625kHz STO clock (16MHz/1024) internally until it
reaches 10 and timer expires. The t
STO
is equal to t
T
x
1024 x 10 = 640µs.
The default value for STODIV is 1024 while the default
value for STOCNT is 0. That means the STO timeout
period is equal 1024 pixel clock cycles. Activity from
the ECU on the control channel shuts off the STO timer
and starts the ETO timer.
ETO Timer
The ETO (end timeout) timer closes the control channel
if the ECU stops communicating for the ETO timeout
period. Configure register REG3[7:4] for both the
MAX9257 and the MAX9258 to select the divide ratio
(ETODIV) for the ETO clock as a function of the pixel
clock (Table 25). The timeout period is determined by
t
f
STODIV STOCNT
STO
CLK
=
⎛
⎝⎜ ⎞
⎠⎟
Ч Ч +
1
1 ( )
28 ______________________________________________________________________________________
Fully Programmable Serializer/Deserializer
with UART/I
2
C Control Channel
REG3[7:4] ETODIV
00XX 16
0100 16
0101 32
0110 64
0111 128
1000 256
1001 512
1010 1024
1011 2048
1100 4096
1101 8192
1110 16,384
1111 32,768
Table 25. ETO Clock Divide Ratio
VIDEO VIDEO HSK
VSYNC_IN
SDI/O ±
CCEN
T1 T2 T3
TX
RX
DOUT_ FROZEN
T1 = TIME TO ENTER CONTROL CHANNEL
T2 = STO TIMEOUT PERIOD
T3 = CONTROL CHANNEL EXIT TIME DUE TO STO
HSK = HANDSHAKING BETWEEN THE MAX9257 AND THE MAX9258
Figure 22. Control Channel Closing Due to STO Timeout