
AD8175
Data Sheet
Rev. B | Page 28 of 40
CMR
CMB
DIFF. R
DIFF. B
INPUT
OVERALL
CM
CMG
DIFF. G
CMENC
AD8175
CMR
CMB
DIFF. R
DIFF. B
OUTPUT
OVERALL
CM
CMG
DIFF. G
VOCM_CMENCON
06478-
022
Figure 49. AD8175 in Middle-of-CAT5-Run Application, CM Encoding On
(Note that in this application, the H and V outputs,
though asserted, are not used)
In this operation mode, the difference Δdiff = VBLK
VOCM_CMENCOFF still adds an output differential voltage,
as described in the previous section.
End-of-CAT5-Run, CM Encoding Turned Off
In this application, each AD8175 output is tapped single-ended
at the positive phase and followed by a fast buffer to drive a
monitor at the end of a CAT5 run (a suitable choice is the
AD8003 set up in a noninverting configuration with gain of
+4). The H and V outputs can then be used to drive the
monitor’s sync inputs directly. The relationship between the
incoming sync-on CM signaling and the H and V syncs is
Table 16. H and V Sync Truth Table (VPOS/VNEG = ±2.5 V)
CMR
CMG
CMB
H
V
0.5
0
Low
High
0
0.5
Low
0.5
0
High
Low
0
0.5
High
The following two statements are equivalent to the truth table
(Table 16) in producing H and V for all allowable CM inputs:
1. H sync is high when the CM of Blue is larger than the CM
of Red.
2. V sync is high when the combined CM of Red and Blue is
larger then the CM of Green.
PROGRAMMING
The AD8175 has two options for changing the programming of
the crosspoint matrix. In the first option, a serial word of 45 bits
can be provided that updates the entire matrix each time. The
second option allows for changing a single output’s programming
via a parallel interface. The serial option requires fewer signals,
but more time (clock cycles) for changing the programming; the
parallel programming technique requires more signals, but
allows for changing a single output at a time, therefore requiring
fewer clock cycles.
Serial Programming Description
The serial programming mode uses the device pins CS, CLK,
SERIN, UPDATE, and SER/PAR. The first step is to enable the
CLK on by pulling CS low. Next, SER/PAR is pulled low to
enable the serial programming mode. The parallel clock WE
should be held high during the entire serial programming
operation.
The UPDATE signal should be high during the time that data is
shifted into the device’s serial port. Although the data still shifts
in when UPDATE is low, the transparent, asynchronous latches
allow the shifting data to reach the matrix. This causes the
matrix to try to update to every intermediate state as defined by
the shifting data.
The data at SERIN is clocked in at every falling edge of CLK. A
total of 45 bits must be shifted in to complete the programming.
A total of five bits must be supplied for each of the nine RGB
output channels—an output enable bit (D4) and four bits (D3 to
D0), which determine the input channel. If D4 is low (output
disabled), the four associated bits (D3 to D0) do not matter,
because no input will be switched to that output.
The most-significant-output-address data is shifted in first, with
the enable bit (D4) shifted in first, followed by the input address
(D3 to D0) entered sequentially with D3 first and D0 last. Each
remaining output is programmed sequentially, until the least-
significant-output-address data is shifted in. At this point,
UPDATE can be taken low, which causes the programming of
the device according to the data that was just shifted in. The
UPDATE latches are asynchronous and when UPDATE is low,
they are transparent.