Maxim Integrated MAX9277, Manual

Page: 59 / 72

HS/VS/DE Inversion
The serializer uses an active high HS, VS, and DE
for encoding and HDCP encryption. Set INVHSYNC,
INVVSYNC, and INVDE in the serializer (registers 0x0D,
0x0E) to invert active low input signals for use with the
GMSL devices. Set INVHSYNC, INVVSYNC, and INVDE
in the deserializer to output active-low signals for use with
downstream devices.
WS/SCK Inversion
The serializer uses standard polarities for I
2
S. Set
INVWS, INVSCK in the serializer (register 0x1B) to invert
opposite polarity signals for use with the GMSL devices.
Set INVWS, INVSCK in the deserializer (register 0x1D) to
output reverse polarity signals for downstream use.
Line-Fault Detection
The line-fault detector in the serializer monitors for line
failures such as short to ground, short to battery, and
open link for system fault diagnosis. Figure 4 shows the
required external resistor connections.
LFLT
= low when
a line fault is detected and
LFLT
goes high when the line
returns to normal. The line-fault type is stored in 0x08
D[3:0] of the serializer. Filter LFLT with the µC to reduce
the detector’s susceptibility to short ground shifts. The
fault detector threshold voltages are referenced to the
serializer ground. Additional passive components set
the DC level of the cable ( Figure 4 ). If the serializer and
GMSL deserializer grounds are different, the link DC volt -
age during normal operation can vary and cross one of
the fault-detection thresholds.
For the fault-detection circuit, select the resistor’s power
rating to handle a short to the battery. In coax mode,
leave the unused line fault inputs unconnected. To detect
the short-together case, refer to Application Note 4709:
MAX9259 GMSL Line Fault Detection
.
Table 20 lists the mapping for line-fault types.
Internal Input Pulldowns
The control and configuration inputs (except 3-level
inputs) include a pulldown resistor to GND. External pull -
down resistors are not needed.
Choosing I
2
C/UART Pullup Resistors
I
2
C and UART open-drain lines require a pullup resistor
to provide a logic-high level. There are tradeoffs between
power dissipation and speed, and a compromise may
be required when choosing pullup resistor values. Every
device connected to the bus introduces some capaci -
tance even when the device is not in operation. I
2
C speci -
fies 300ns rise times (30% to 70%) for fast mode, which is
defined for data rates up to 400kbps (see the I
2
C specifi -
cations in the
Electrical Characteristics
table for details).
To meet the fast-mode rise-time requirement, choose the
pullup resistors so that rise time t
R
= 0.85 x R
PULLUP
x
C
BUS
< 300ns. The waveforms are not recognized if the
transition time becomes too slow. The device supports
I
2
C/UART rates up to 1Mbps.
Table 20. Line Fault Mapping
REGISTER ADDRESS BITS NAME VALUE LINE FAULT TYPE
0X08
D[3:2] LFNEG
00 Negative cable wire shorted to supply voltage
01 Negative cable wire shorted to ground
10 Normal operation
11 Negative cable wire disconnected
D[1:0] LFPOS
00 Positive cable wire shorted to supply voltage
01 Positive cable wire shorted to ground
10 Normal operation
11 Positive cable wire disconnected
MAX9277/MAX9281 3.12Gbps GMSL Serializers for Coax or
STP Output Drive and LVDS Input
www.maximintegrated.com
Maxim Integrated │ 59