PRELIMINARY
CM2031
Active Local Pullup Control
Hotplug Output Pullup Logic
For a system where a low voltage GPIO signal needs
to control the HOTPLUG pin (i.e. if the local system
needs to boot up before asserting HOTPLUG) the
ASIC GPIO can be connected directly to the
HOTPLUG_DET_IN pin to control the 5V pullup "on"
and "off." A logic "low" on HOTPLUG_DET_IN will dis•
able the 5V pullup, and a logic "high" will enable the
pullup. (NOTE: If the ASIC Power-ON Reset {POR}
default of the GPIO is high-impedance or defaults to an
input, then the designer should include a weak pull-
down on the GPIO to eliminate any POR glitches.)
The CM2031 includes flexible circuitry for active or
passive control of the HDMI Sink’s Hotplug Present
Output line by integrating the 1kΩ pullup resistor.
Section 8.5 of the HDMI Specification allows the HDMI
Sink to pulse the HotPlug line "low" for at least
100msec to indicate to the Source that the EEPROM
should be re-read. This function can be implemented
with a few discrete components as shown in Figure 7.
+5V_HDMI (Pin 18)
1kΩ
HOTPLUG (Pin 19)
5V_SUPPLY
ASIC
GPIO
ASIC
GPIO
Figure 7. Typical Discrete HPD Switching Circuit
1kΩ
The Hot Plug Detect circuit of the CM2031 is specifi•
cally designed to provide this "pulse" capability and still
pass CTS testing requirements.
HOTPLUG_OUT
CM2031
When
a
logic "high" is applied to the
HOTPLUG_DET_IN pin, an internal switch enables the
1kΩ pull-up. When a logic "low" is sensed on this pin,
the 1kΩ logic resistor is disconnected, and a weak pull-
down ensures a valid low output on the HDMI cable.
Figure 8. Simplified CM2031 HPD Circuit
5V Passive Pullup
In the most basic implementation, where HOTPLUG is
to be asserted only when the HDMI +5V supply is
applied, simply tie HOTPLUG_DET_IN to the +5V sup•
ply and connect HOTPLUG_DET_OUT to HDMI Con•
nector (Pin 19).
Local Power Supply Pullup Passive
For a system that needs to inhibit the HOTPLUG signal
when the local ASIC low voltage supply
("LV_SUPPLY" on CM2031) has been powered, the
designer can simply connect HOTPLUG_DET_OUT to
the
HDMI
Connector
(Pin
19)
and
tie
HOTPLUG_DET_IN to the "LV_SUPPLY" which can
be 1.5V, 1.8V, 2.5V, etc. Then the internal 1kΩ pullup
will be enabled between HOTPLUG_DET_OUT and
5V_SUPPLY.
If a weak pullup is used on HOTPLUG_DET _IN, then
this still allows dynamic switching by the local ASIC
while still retaining the isolation/backdrive protection on
this pin.
© 2005, 2006California Micro Devices Corp. All rights reserved.
8/8/2006 430 N. McCarthy Blvd., Milpitas, CA 95035-5112
✍
Tel: 408.263.3214
✍
Fax: 408.263.7846
✍
www.calmicro.com
7
CALMIRCO [ CALIFORNIA MICRO DEVICES CORP ]
