How to decode communication

[Christopher4187]

I'm still kind of lost but seem to be making a little progress. I can see that the entire packet takes 20mS to transmit. It's hard to tell where one piece of data ends and the other begins. I can see the data change when I press buttons on the controller but some of the data isn't used for this application. In other words, those bits/bytes are just taking up space but must be included when the packet is transmitted.

Perhaps this will help you guys help me. I concentrated on the ones digit for the home team score. I think it takes 750uS to transmit the ones digit and I based that assumption on when the edge falls to when it rises again at the end. However, some of the data takes about 500uS. Is it safe to assume that it takes 750uS for a byte and maybe 500uS for a bit?

To duplicate the packet (I'm starting with the ones digit), I have the data from the PIC going to the input of a ULN2003A. On the output side I'm using a 10K pullup and then measuring it with the scope. One problem I'm having is that I can't quite get the timing right. I've attached two pictures that show my problem. The first picture is of the source. I'm trying to duplicate what is seen here. In the middle (-250uS from center to +500uS from center) is the number 2.

Here is my attempt to make the number 2. As you can see, I had to adjust the sec/div to 100uS and the second pulse in the number two isn't the same as the source.

Regarding the data being inverted, what is the normal way? High to low or low to high?

I've tried adjusting my settings but nothing seems to help. The relevant settings are:

RCSTA1 = $90 
TXSTA1 = $24 
DEFINE HSER_BAUD 300
DEFINE HSER_CLROERR 1 ' Clear overflow automatically
BAUDCON1 = %00111000

And then I send the data like this:


MAINLOOP:
HSEROUT [dec 2]
PAUSE 100
GOTO MAINLOOP

[Jerson]

From the images, I do not think it is an UART transmission. Can you zoom out the source capture a little so that you center the '2' and we can see around it a bit more detail?

[Christopher4187]

I've attached pictures of the PCB, a picture of the #2 zoomed in and a picture of the #2 zoomed out.

[Jerson]

Looking at the components, it might be a current loop signalling. Is it?

Are there any communications related components below the LCD ? Cant see them in the photo.

[Christopher4187]

There's nothing under the LCD. What you see is what you get. Correct me if I'm wrong but it can't be a current loop because I have nothing connected to the output except the scope probe.

[Christopher4187]

The signal output appears to be coming from a 2N3417 (collector), which also appears to be in parallel with a TIP30C (collector).

[Christopher4187]

Something else popped into my head. The time between the start of each byte is exactly 1,250uS. The time it takes to transmit the total packet is 20mS, which means there are 16 digits. Can I do all of this manually? To be more specific, can I use GOSUB's for each number and just specify exactly how long I need the pulses to be? The data is predictable and I'm not seeing anything that doesn't look strange. There are only numbers transmitted and they are 0-9. My thought is something like this:

MAINLOOP:

'GATHER NUMBERS TO BE TRANSMITTED

SELECT CASE D0
    CASE 0
        GOSUB ZERO
    CASE 1
        GOSUB ONE
END SELECT

SELECT CASE D1
    CASE 0
        GOSUB ZERO
    CASE 1
        GOSUB ONE
END SELECT


SELECT CASE D2
    CASE 0
        GOSUB ZERO
    CASE 1
        GOSUB ONE
END SELECT

......

SELECT CASE D15
    CASE 0
        GOSUB ZERO
    CASE 1
        GOSUB ONE
END SELECT

PAUSE 5

GOTO MAINLOOP

.....

ZERO:
DO3=1
PAUSEUS 550
DO3=0
PAUSEUS 75
DO3=1
PAUSEUS 50
DO3=0
PAUSEUS 575
RETURN

ONE:
DO3=1
PAUSEUS 50
DO3=0
PAUSEUS 75
DO3=1
PAUSEUS 175
DO3=0
PAUSEUS 300
DO3=1
PAUSEUS 50
DO3=0
PAUSEUS 600
RETURN

TWO:
DO3=1
PAUSEUS 250
DO3=0
PAUSEUS 75
DO3=1
PAUSEUS 150
DO3=0
PAUSEUS 75
DO3=1
PAUSEUS 250
DO3=0
PAUSEUS 450
RETURN

THREE:
DO3=1
PAUSEUS 400
DO3=0
PAUSEUS 150
DO3=1
PAUSEUS 250
DO3=0 
PAUSEUS 450
RETURN

FOUR:
DO3=1
PAUSEUS 75
DO3=0
PAUSEUS 75
DO3=1
PAUSEUS 150
DO3=0
PAUSEUS 150
DO3=1
PAUSEUS 250
DO3=0
PAUSEUS 550
RETURN

FIVE:
DO3=1
PAUSEUS 150
DO3=0
PAUSEUS 75
DO3=1
PAUSEUS 150
DO3=0
PAUSEUS 75
DO3=1
PAUSEUS 325
DO3=0
PAUSEUS 475
RETURN

SIX:
DO3=1
PAUSEUS 150
DO3=0
PAUSEUS 75
DO3=1
PAUSEUS 475
DO3=0
PAUSEUS 550
RETURN

SEVEN:
DO3=1
PAUSEUS 325
DO3=0
PAUSEUS 300
DO3=1
PAUSEUS 150
DO3=0
PAUSEUS 475
RETURN

EIGHT:
DO3=1
PAUSEUS 800
DO3=0
PAUSEUS 450
RETURN

NINE:
DO3=1
PAUSEUS 325
DO3=0
PAUSEUS 150
DO3=1
PAUSEUS 325
DO3=0
PAUSEUS 450
RETURN