Analog Devices ADV7850 Hardware Manual page 272

length count in 27 MHz (XTAL) clocks.
Note: chx is CH1 or CH2 in the above descriptions, representing channel 1 and channel 2 related registers.
By interpreting these four parameters, it is possible to derive the applied video signal horizontal and vertical resolution information and
determine its standard.
In ADV7850, there are three operational modes for the STDI block:
Continuous mode:
•
The STDI block performs continuous measurements on a lock/unlock basis and updates the corresponding I
on the lock status bit (stdi_dvalid).
• Real-time continuous mode:
The STDI block performs continuous measurement regardless of the lock/unlock basis and always updates real-time
measurement data to the corresponding I
• Single shot mode:
The STDI block waits for a trigger (0 to 1 transition on chx_trig_stdi) to start the measurements. Single-shot mode can be useful
in complex systems where the scheduling of functions is important.
A data valid flag, chx_stdi_dvalid, is provided, which is based on the status of the horizontal/vertical lock of the block and is held low
during the measurements. The four parameters should only be read after the chx_stdi_dvalid flag has gone high for the continuous/single
shot mode. In real-time continuous mode, the ADV7850 allows the user to monitor the real-time timing measurement regardless of the
chx_stdi_dvalid flag. Refer to Section
Notes:
• Synchronization type pulses include horizontal synchronization, equalization and serration pulses, and Macrovision pulses.
• Macrovision pseudo synchronization and AGC pulses are counted by the STDI block in normal readback mode. This does not
prohibit the identification of the video signal.
• chx_trig_stdi is not self clearing. The measurements are only started upon setting chx_trig_stdi. This means that after setting it,
it must be cleared again by writing a 0 to it. This second write (to clear it) can be done at any time and does not have any effect
on running measurements. It also does not invalidate previous measurement results.
The ADV7850 only measures those parameters, but does not take any action based upon them. The part does not reconfigure
•
itself. To avoid unforeseen problems in the scheduling of a system controller, the part merely helps to identify the input.
•
Since real-time continuous mode provides the capability to monitor the real-time measurement data regardless of the block lock
status, the user should be aware that the timing readback values may not be a valid readback measurement in this mode.
ch1_stdi_cont, Addr 44 (CP), Address 0x86[1]
This control is used to set the synchronization source polarity detection mode for sync channel 1 STDI.
Function
ch1_stdi_cont
0
1 
ch2_stdi_cont, Addr 44 (CP), Address 0x42[1]
This control is used to select the sync channel 2 STDI mode of operation.
Function
ch2_stdi_cont
0
1 
Rev. A May 2012
2 C registers.
9.7.3.4 for information on the readback values.
Description
Sync channel 1 STDI works in one-shot mode (triggered by 0 to 1 transition on ch1_trig_sspd)
Sync channel 1 STDI works in continuous mode
Description
Sync channel 2 STDI block operates in single-shot mode. 0 to 1 transition on ch2_trig_stdi
triggers measurement of sync channel 2 STDI block.
Sync channel 2 STDI runs in continuous mode.
272
ADV7850
C registers based
2
P
P