10-10-2020, 08:05 PM
HI Stephen
I should have explained that.
Jeffrey is correct it is clock cycles. I will leave them there as I think it makes it clearer what is happening.
The number that you see on the left of the bottom line of the display is the length of that parameter in clock cycles. The rotary encoder will change this number up or down
The length of that parameter in time is calculated from the number of clock cycles and displayed to the right.
So the duration of H SYNC is 79 clock cycles or 8.947 uS.
The reason that I have both displayed is that all parameters that changes the number of clock cycles in a line are interdependent. (front porch, H sync, back porch, right crop and left crop)
In a standard the length of a full line in time is fixed. It can be got by 1 / (number of frames * number of lines) the result been in seconds.
For 405 lines it is 1/(25*405) = 0.0000987654 or 98.7654 uS (lets say 98.77 uS)
If we were doing 405 lines the total number of clock cycles in a line must always take exactly 98.77 uS to complete.
If we had 100 cycles in a line each cycle would take 0.9877 uS.
If we were then to increase the number of cycles in say H SYNC by 20 there will now be a total of 120 cycles in a line.
These 120 cycles will have to fit in 98.77 uS. So each cycle will have to be shorter in duration. Each cycle will now take 0.8230 uS.
So by increasing the length of H SYNC all other parameters (front porch, back porch and active line) gets shorter.
Setting a standard on it is a bit like setting the convergence on a delta gun CRT but much easier.
The number of cycles in a full line must always be even. This is to ensure that the broad pulses and equalising pulses occur in the correct places.
At the point of setting a standard if the number of cycles are not even 1 cycle is either added to or taken from H SYNC to make the total number of cycles in a line even.
So it is possible to see the number of clock cycles in H SYNC change by +/- 1 from what it was set at.
Frank
I should have explained that.
Jeffrey is correct it is clock cycles. I will leave them there as I think it makes it clearer what is happening.
The number that you see on the left of the bottom line of the display is the length of that parameter in clock cycles. The rotary encoder will change this number up or down
The length of that parameter in time is calculated from the number of clock cycles and displayed to the right.
So the duration of H SYNC is 79 clock cycles or 8.947 uS.
The reason that I have both displayed is that all parameters that changes the number of clock cycles in a line are interdependent. (front porch, H sync, back porch, right crop and left crop)
In a standard the length of a full line in time is fixed. It can be got by 1 / (number of frames * number of lines) the result been in seconds.
For 405 lines it is 1/(25*405) = 0.0000987654 or 98.7654 uS (lets say 98.77 uS)
If we were doing 405 lines the total number of clock cycles in a line must always take exactly 98.77 uS to complete.
If we had 100 cycles in a line each cycle would take 0.9877 uS.
If we were then to increase the number of cycles in say H SYNC by 20 there will now be a total of 120 cycles in a line.
These 120 cycles will have to fit in 98.77 uS. So each cycle will have to be shorter in duration. Each cycle will now take 0.8230 uS.
So by increasing the length of H SYNC all other parameters (front porch, back porch and active line) gets shorter.
Setting a standard on it is a bit like setting the convergence on a delta gun CRT but much easier.
The number of cycles in a full line must always be even. This is to ensure that the broad pulses and equalising pulses occur in the correct places.
At the point of setting a standard if the number of cycles are not even 1 cycle is either added to or taken from H SYNC to make the total number of cycles in a line even.
So it is possible to see the number of clock cycles in H SYNC change by +/- 1 from what it was set at.
Frank
