Rainbow Electronics MAX9595 - Manual (Page 16)

MAX9595
2-Wire Interface Data Format
I 2 C Compatibility
The MAX9595 is compatible with existing I 2 C systems.
SCL and SDA are high-impedance inputs. SDA has an
open drain that pulls the bus line to a logic-low during
the 9th clock pulse. Figure 5 shows a typical I
2 C inter-
face application. The communication protocol supports
the standard I
2 C 8-bit communications. The MAX9595
address is compatible with the 7-bit I 2 C addressing
protocol only; 10-bit format is not supported.
Digital Inputs and Interface Logic
The I 2 C-compatible, 2-wire interface has logic levels
defined as V IL = 0.8V and V IH = 2.0V. All of the inputs
include Schmitt-trigger buffers to accept low-transition
interfaces. The digital inputs are compatible with 3V
CMOS logic levels.
Programming
Connect DEV_ADDR to ground to set the MAX9595
write and read address as shown in Table 2.
Data Register Writing and Reading
Program the SCART video and audio switches by writ-
ing to registers 00h through 0Dh. Registers 00h through
0Eh can also be read, allowing read-back of data after
programming and facilitating system debugging. The
status register is read-only and can be read from
address 0Eh. See Tables 3–12 for register program-
ming information.
INTERRUPT_OUT Signal
INTERRUPT_OUT is an open-drain output that
becomes high impedance when a change in any of the
slow-switch signals occurs. Clear INTERRUPT_OUT by
setting bit 4 of register 01h low.
Applications Information
Hot-Plug of SCART Connectors
The MAX9595 features high-ESD protection on all
SCART inputs and outputs, and requires no external
transient-voltage suppressor (TVS) devices to protect
against floating chassis discharge. Some set-top boxes
have a floating chassis problem in which the chassis is
not connected to earth ground. As a result, the chassis
can charge up to 500V. When a SCART cable is con-
nected to the SCART connector, the charged chassis
can discharge through a signal pin. The equivalent cir-
cuit is a 2200pF capacitor charged to 311V connected
through less than 0.1Ω to a signal pin. The MAX9595 is
soldered on the PC board when it experiences such a
discharge. Therefore, the current spike flows through
the ESD protection diodes and is absorbed by the sup-
ply bypass capacitors, which have high capacitance
and low ESR.
To better protect the MAX9595 against excess voltages
during the cable discharge condition, place an addi-
tional 75Ω resistor in series with all inputs and outputs
to the SCART connector. For harsh environments where
±15kV protection is needed, the MAX4385E and
MAX4386E single and quad high-speed op amps fea-
ture the industry’s first integrated ±15kV ESD protection
on video inputs and outputs.
Audio/Video Switch for Dual SCART Connector
16 ______________________________________________________________________________________
μC
SCL
SCL
SDA
V
VID
MAX9595
SCL
SDA
V
DD
SCL
SDA
V
DD
DEVICE 2
DEVICE 1
SDA
Figure 5. Typical I 2 C Interface Application
ADDRESS PIN
STATE
WRITE
ADDRESS
READ ADDRESS
V VID 96h 97h
GNDVID 94h 95h
Table 2. Slave Address Programming
S
Slave
Address
A
Register
Address
A Data2 A P
Write and Read Mode
S = Start Condition, A = Acknowledge, P = Stop Condition