LMH0387
SNLS315H –APRIL 2010–REVISED AUGUST 2015
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7.4 Device Functional Modes
SPI register access is required while operating the LMH0387 in the input mode. The equalizer launch amplitude
fine tuning must be set to nominal through the SPI for correct equalizer operation. To do this, write 30h
(“00110000 binary”) to SPI register 02h. The SPI registers provide access to many other useful LMH0387
features while in the input mode.
To configure the LMH0387 in the output mode, the cable driver must be enabled. The equalizer may either be
disabled for power savings or enabled to provide a loopback path for the data being transmitted. For the normal
output mode (equalizer disabled for power savings) follow these steps:
1. Disable the equalizer by forcing it to sleep through the SPI. To do this, write “10” (force sleep) to bits [4:3] of
SPI register 00h.
2. Enable the cable driver by pulling the TX_EN pin high.
7.5 Programming
The LMH0387 3 Gbps HD/SD SDI Configurable I/O Adaptive Cable Equalizer / Cable Driver is used at the input
or output port of digital video equipment. It is designed to allow the sharing of a single BNC connector for either
input or output. The LMH0387 must be configured in either the output mode as a cable driver, or the input mode
as an equalizer.
7.5.1 Output Mode (Cable Driver)
To configure the LMH0387 in the output mode, the cable driver must be enabled. The equalizer may either be
disabled for power savings or enabled to provide a loopback path for the data being transmitted. For the normal
output mode (equalizer disabled for power savings) follow these steps:
1. Disable the equalizer by forcing it to sleep through the SPI. To do this, write “10” (force sleep) to bits [4:3] of
SPI register 00h.
2. Enable the cable driver by pulling the TX_EN pin high.
To configure the LMH0387 for the output mode with the loopback path, the equalizer can be enabled in output
mode by writing either “01” (auto sleep – default) or “00” (never sleep) to bits [4:3] of SPI register 00h. In this
case, the LMH0387 input/output mode may be configured simply by toggling the TX_EN pin because the
equalizer remains active in either mode (TX_EN set low for input mode and high for output mode).
7.5.2 Input Mode (Equalizer)
To configure the LMH0387 in the input mode, the equalizer must be enabled and the cable driver must be
disabled as described in the following steps:
1. Disable the cable driver by pulling the TX_EN pin low.
2. Enable the equalizer by setting the sleep mode through the SPI to either auto sleep or disabled (never
sleep). To do this, write either “01” (auto sleep – default) or “00” (never sleep) to bits [4:3] of SPI register
00h.
3. Set the equalizer launch amplitude fine tuning to the nominal setting through the SPI. To do this, write 30h
(“00110000” binary) to SPI register 02h.
7.5.3 Input Mode (Equalizer) SPI Register Access
SPI register access is required for correct input mode (equalizer) operation. The SPI registers provide access to
all of the equalizer features along with a cable length indicator, programmable output common mode voltage and
swing, and launch amplitude optimization. There are four supported 8-bit registers in the device (see SPI
Registers).
Note: The SPI_EN pin must always be pulled high while using the LMH0387 in the input mode (equalizer), and
may optionally be pulled high while using the LMH0387 in the output mode (cable driver) as well.
7.5.3.1 SPI Write
The SPI write is shown in Figure 2. The MOSI payload consists of a “0” (write command), seven address bits,
and eight data bits. The SS signal is driven low, and the 16 bits are sent to the LMH0387's MOSI input. Data is
latched on the rising edge of SCK. The MISO output is normally tri-stated during this operation. After the SPI
write, SS must return high.
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