Cec Api Control; Cec Reference Clock Calibration; Cec Programming Interface (Cpi) - THOMSON 22E92NH22 Service Manual

SiI9185A 3:1 HDMI 1.3 Switch
Preliminary Data Sheet

CEC API Control

There is hardware assistance in the SiI9185A for CEC control that makes the software development for CEC much
easier. CEC control has been implemented according to the internal Silicon Image CEC API (CPI ) specification.
The CEC signal has two modes of operation:
1. Pass-through mode: In this mode, an external microcontroller can control the CEC level by using the CEC_D
pin. The CEC API function in the SiI9185A is not used.
2. CEC API mode: In this mode, the SiI9185A performs decoding when acting as a follower, and a high-level
command interface when acting as an initiator.
Pass-through mode is engaged under the following conditions:
•
When the SiI9185A is working in Standalone mode, or
•
When the SiI9185A is working in I

CEC Reference Clock Calibration

An on-chip ring oscillator is used to send and receive CEC data while meeting the CEC timing specification. However,
the ring oscillator frequency can vary on a per device basis, based on manufacturing variables. Therefore, it is necessary
to calibrate this internal ring oscillator by applying an externally driven pulse of 10 ms to the CEC_D pin. The procedure
for applying this calibration signal is:
1. The host processor should set the CEC_D pin high before starting the calibration cycle.
2. The host processor starts the calibration cycle by setting the CALIB bit in local I
bit is self-resetting.
3. The host processor should wait for at least 100 ns after writing the CALIB bit.
4. The host processor should then cause the CEC_D pin to go through a high-to-low transition. The signal should
stay low for a period of 10 ms ±1%, and then transition back high.
5. At this point calibration is complete.
6. The calibration cycle will be repeated each time the host writes a '1' to the CALIB bit.
A counter is used to count the number of ring oscillator clocks in this 10 ms pulse, and the frequency of the ring
oscillator is determined from this count. This is used as the time base to accurately send and receive CEC commands
according to the CEC specification. Note that unless the calibration pulse is properly applied to the SiI9185A and the
calibration cycle is properly completed, the CEC logic will NOT operate correctly. The host should complete the
calibration cycle before setting the CEC enable bit in the local I
The oscillator used in the CEC timing mechanism may vary slightly with temperature. It is recommended that as a
precaution the CEC reference clock calibration process be repeated for every 15°C of change. For example, it may be
periodically recalibrated approximately every 10 minutes.
In standalone applications where CEC-relay mode is used, the incoming CEC timing is measured using the internal
oscillator clock to reproduce the correct output timing. For example, if the START period of CEC_D is measured to be
some number of internal oscillator clocks, that number is used as the basis to re-shape the CEC output timing. Therefore,
in CEC-relay mode a calibration pulse is not required.

CEC Programming Interface (CPI)

The CEC application solution involves both low-level and a high-level components. For low-level components, the low-
level CEC protocol is handled by the slave I
CEC software source code allows command strings to be exchanged over the I
For development, Silicon Image provides Windows-based software tools, including a kit that allows a PC to be used to
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generate I C commands over any USB 1.1-capable port.
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The I C register set used for this solution is referred to as CEC Programming Interface or just CPI. This standard register
set is used across all Silicon Image devices and applications, both software and hardware.
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2
C Control mode but the CEC enable bit is set to 0 (offset 0x08 bit 6)
2
C.
2
C interface of the SiI9185A. For high-level components, the Silicon Image
© 2007 Silicon Image, Inc. CONFIDENTIAL
Silicon Image, Inc.
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C offset 0x09 bit 0 to 1. This
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C interface as discussed above.
SiI-DS-1016-0.80