Rainbow Electronics MAX9258 - Manual (Page 25)

tracks and passes the spread to the data and clock out-
puts. The PRATE range of 00 and 01 (5MHz ≤ PCLK ≤
20MHz) supports all the spread options. The PRATE
range of 10 and 11 (20MHz ≤ PCLK ≤ 70MHz) requires
that the spread be 2% or less.
Pixel Clock Jitter Filter
The MAX9257 has a PLL to filter high-frequency pixel
clock jitter on PCLK_IN. The FPLL can be bypassed by
writing 1 to REG4[2]. The FPLL improves the
MAX9258’s data recovery by filtering out the high-fre-
quency components from the pixel clock that the
MAX9258 cannot track. The 3db bandwidth of the FPLL
is 100kHz (typ).
LVDS Output Preemphasis (SDO±)
The MAX9257 features programmable preemphasis
where extra current is added when the LVDS outputs
transition on the serial link. Preemphasis provides addi-
tional current to the normal drive current. For example,
20% preemphasis provides 20% greater current than
the normal drive current. Current is boosted only on the
transitions and returns to the normal drive current after
switching. Select the preemphasis level to optimize the
eye diagram. Preemphasis boosts the high-frequency
content of the LVDS outputs to enable driving greater
cable lengths. The amount of preemphasis is pro-
grammed in REG12[7:5] (Table 21).
VSYNC, HSYNC, and Pixel Clock Polarity
PCLK: The MAX9257 is programmable to latch data on
either rising or falling edge of PCLK. The polarity of
PCLKOUT at the MAX9258 can be independent of the
MAX9257 PCLK active edge. The polarity of PCLK can
be programmed using REG4[5] of the MAX9257 and
the MAX9258.
VSYNC: The MAX9257 and the MAX9258 enter control
channel on the falling edge of VSYNC. The default reg-
ister settings are VSYNC active falling edge for both the
MAX9257 and the MAX9258. If the VSYNC active edge
is programmed for rising edge at the MAX9257, the
MAX9258 VSYNC active edge must also be pro-
grammed for rising edge to reproduce VSYNC rising
edge at the MAX9258 output. However, matching the
polarity of the VSYNC active edge between the
MAX9257 and the MAX9258 is not a requirement for
proper operation.
HSYNC: HSYNC active-edge polarity is programmable
for the MAX9258.
General Purpose I/Os (GPIOs)
The MAX9257 has up to 10 GPIOs available. GPIO8
and GPIO9 are always available while GPIO[0:7] are
available depending on the parallel-word width (Table
22). If GPIOs are not available, the corresponding GPIO
bits are not used.
MAX9257/MAX9258
______________________________________________________________________________________ 25
Fully Programmable Serializer/Deserializer
with UART/I
2
C Control Channel
FREQUENCY
TIME
f SPREAD (MAX)
f PCLK_IN
f SPREAD (MIN)
1/f SSM
Figure 21. Simplified Modulation Profile for the MAX9257/MAX9258
PRATE (REG1[7:6]) SPREAD (%)
00 Off
01 ±2
10 Off
11 ±4
Table 17. MAX9258 Spread
PRATE
(REG1[7:6])
MODULATION RATE f SSM RANGE (kHz)
00 PCLK/312 16 to 32
01 PCLK/520 19.2 to 38.5
10 PCLK/1040 19.2 to 38.5
11 PCLK/1248 32 to 56
Table 18. MAX9258 Modulation Rate
REG1[7:5] SPREAD (%)
000 Off
001 ±1.5
010 ±1.75
011 ±2
100 Off
101 ±3
110 ±3.5
111 ±4
Table 19. MAX9257 LVDS Output Spread