User Programmable Standards Converter

[ppppenguin]

When you look at the data sheets for those modulators they are not the easiest of things to fully understand. The data for programming them is split awkwardly between different bytes. When I looked at Frank's VHDL I dimly remember suggesting that it would be easier to let the VHDL tools do more of the work, instead of laboriously assembling all the data by hand. Here's an example from the original Hedghog:

Code:

constant  CH4_CF_DATA      : ic2_data_array := ("0001111011100011", "1011000110000000", "0001110100100011", "1011000010000000"); -- modulators channel 4

I'd go crazy if I had to do that for multiple channels and different standards. Far too easy to make mistakes. Express things in a way that humans can understand and let the tools do the work.

[Richard_FM]

As far as I can remember 819 lines in France were only broadcast on VHF.

UHF was used when the second channel started in the mid 1960s, and started to use SECAM in 1967.

TF1 only started to use SECAM as the 819 line transmitters were switched over to SECAM from the mid 1970s, I think some rural areas didn't switch until the early 1980s.

[`FRANK.C]

The bit map for programming the modulator is all over the place.
Map shown below for the video modulator.

Code:

  Video_C1.7 = 1
  Video_C1.6 = 0
  Video_C1.5 = SO
  Video_C1.4 = LOP
  Video_C1.3 = PS
  Video_C1.2 = X3
  Video_C1.1 = X2
  Video_C1.0 = SYSL

  Video_C0.7 = PWC
  Video_C0.6 = OSC
  Video_C0.5 = ATT
  Video_C0.4 = SFD1
  Video_C0.3 = SFD0
  Video_C0.2 = SREF
  Video_C0.1 = X5
  Video_C0.0 = X4

  Video_FM.7 = 0
  Video_FM.6 = TPEN
  Video_FM.5 = N11
  Video_FM.4 = N10
  Video_FM.3 = N9
  Video_FM.2 = N8
  Video_FM.1 = N7
  Video_FM.0 = N6

  Video_FL.7 = N5
  Video_FL.6 = N4
  Video_FL.5 = N3
  Video_FL.4 = N2
  Video_FL.3 = N1
  Video_FL.2 = N0
  Video_FL.1 = X1
  Video_FL.0 = X0

Hopefully when I get finished anyone needing to setup a channel will not realise that.

What I am working towards is having a number of presets. Each preset will have associated with it a standard and also a channel.

Instead of selecting a channel number from a set number of channels the channel required will need to be setup by selecting a number of options. Such as Frequency, negative/positive video, AM/FM sound, sound separation,  etc.
The options will be easily selected using the LCD and rotary encoders. The microcontroller will take care of changing the options into the gobbledygook needed to program the modulators.
This will release most of the capability's of the modulator to the user rather been stuck with a limited amount of preset channels. On each preset the standard converter can be switched off so it can be used as a modulator only.

At least that is the plan.

Frank

[ppppenguin]

All sounds sensible to me. Let computers do the work that they are good at.

While it's probably easier in a microprocessor it's entirely possible to do this sort of thing in VHDL too. Just declare a signal for each important parameter. Use a CASE statement to set the value of each parameter for each channel and concatenate the results using "&" to make the programming strings.

[`FRANK.C]

I have spent some time on the modulator side of this project. So far I have:
30 to 900 MHz in 250 KHz steps vision modulator.
Selectable Positive video modulation AM sound / Negative video modulation FM sound
Selectable 3.5, 4.5, 5.5, 6 and 6.5 MHz sound. 3.5 MHZ is AM only

That will cover most channels. The only one that I can think of that it wont is the French system E. Can anyone think of any others?
I may try doing a special for system E but I am not sure how well it will fit with the available dividers. I haven't done the maths on it yet.

The MC44BS373 data sheet don't explicitly state the UHF frequency range. That is something that I have been caught out with before.
It just says "Channel 21–69 UHF operation" It also says "VHF range possible by internal dividers (30–450 MHz)"
The smallest divider is 2. So in order to be able to do 450 MHz the UHF oscillator will have to extend to 900 MHZ which is above channel 69.
The dividers are 16, 8, 4 and 2. In order to cover the range 30 to 450 MHz without there been any holes in it the UHF oscillator will need to reach 450 MHz at its lowest setting.
So I have set the range of the UHF oscillator at 450 MHz to 900 MHZ. My example works fine with those limits.

Photos below of some menu positions with it set up for System A 405 lines Channel 2
The number of active lines is per field. The menu is in rough form yet. There is some tweaking to be done.

Frank

[Freya]

Looking nice on that display.
What is the significance of the first number on the 13 front porch, 79 H sync and 70 back porch ?

[ppppenguin]

Must be length in clock cycles. Possibly on the display for debug purposes.

[`FRANK.C]

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

[Freya]

Thanks for the explanation, makes perfect sense of course.

[`FRANK.C]

I had ruled out doing 30/60 Hz as I felt the converter would do a really terrible job of it.
Yesterday I received a 525 line monitor so today hooked it up to see what 30/60 Hz looked like out of the converter.
As expected stills are good. But any movement is jittery. However it is not quite as bad as I had imagined.
I have seen nearly as bad at times on some satellite channels. So I think I will leave the ability to do 30/60 Hz field's in even though it is not so good.

Frank