Looking for any code to set the MT8808's switches...

Other Hardware General Electronics
1

Experts,

In building my Ethernet/RJ-11/STP/UTP cable tester, I need a switch like the mt8808. I grabbed 5 of them to dabble with, and have not seen a single line of code out there beyond the C64 emulator with a Mega here. I'm fishing to see if there is anyone else who has used the switch, or any others in the series.

The tester will send a variety of signals (& sources) down any of up to 8 wires. The MT8808 allows me to set up the sources on one axis, and the pin selection on the other. Because the IO is limited to 15mA, output of the switches will be boosted to make it to the other end, and the inputs padded down before going into the switch for routing to the uC.

Here is how I have determined the signaling should work:

  • Set RESTE LOW.
  • Set AX0-2 and AY0-2 to the desired switch.
  • Set STROBE HIGH.
  • Set DATA HIGH/LOW (desired).
  • Set STROBE LOW (latches, asynchronously).

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I'm figuring on just making a function to set the switch, one line of code as above at a time. Control input seems to be tolerant of anything from 3.3v to Vdd (15v max).

Any gotchas? I don't want to blow them up! :slight_smile:

2

holesflow:
In building my Ethernet/RJ-11/STP/UTP cable tester, I need a switch like the MT8808.

So you posted a link to your own computer. :roll_eyes:

3

Paul__B:
So you posted a link to your own computer. :roll_eyes:

Dohh! Well, for those that can't come over, this may work better... yes? It's just the datasheet. I stupidly copied the URI field from browser that was viewing the PDF...

4

Perhaps this is what you meant to post:

https://www.microsemi.com/document-portal/doc_view/127033-mt8808-datasheet-sep11

5

If anyone has gotten this far, great!

The first thing I needed to do in using the MT8808 (or any in the series) is decode an address (char) to bits (octal), as there are 3 X (rows), and 3 Y (columns) address bits. 8 x 8 ins/outs means 3 bits defines one or more of 8. Simple.

But in code, I wouldn't be doing this hard coded, like "Turn switch at 101 x 110 on!". In reality, they would be known as 1-8, as that is how the cable lines are known. There is no pin 010 or "o" on STP/UTP.
So here is my first draft of how to convert between human into binary (octal) addresses:

[...]
int intX = 0; // 0-7
int intY = 0; // 0-7
intX = (int)random(0,8); // 0-7
intY = (int)random(0,8); // 0-7
SetSwitch((char)intX,(char)intY,'1');
[...]
void SetSwitch(byte bX, byte bY, byte val) 
{
  const char* cArrayX[3];
  const char* cArrayY[3];
  for (byte iX = 0; iX < 3; iX++)
  {
    cArrayX[iX] = bitRead(bX, iX)? "1" : "0";
  }
  for (byte iY = 0; iY < 3; iY++)
  {
    cArrayY[iY] = bitRead(bY, iY)? "1" : "0";
  }
}
[...]

The above is fine, right? The full source has a ton of Serial.print[ln] debuging, but is there a better/simpler way to break down the number into bits?

6

holesflow:
The above is fine, right? The full source has a ton of Serial.print[ln] debuging, but is there a better/simpler way to break down the number into bits?

Yes, just pull out the bits:

digitalWrite (AY2, (yaddress >> 2) & 1) ;
digitalWrite (AY1, (yaddress >> 1) & 1) ;
digitalWrite (AY0, (yaddress >> 0) & 1) ;

Even simpler if you declare an array of pin numbers:

void switch_switch (int xaddress, int yaddress, boolean sense)
{
  for (byte i = 0 ; i <= 2; i++)
  {
    digitalWrite (AY[i], (yaddress >> i) & 1) ;
    digitalWrite (AX[i], (xaddress >> i) & 1) ;
  }
  digitalWrite (STROBE, HIGH) ;
  digitalWrite (DATA, sense) ;
  digitalWrite (STROBE, LOW) ;
}
7

Well, after setting up a test on breadboard, it is behaving strangely. I'll take the rather involved test setup and create a schematic & show code. Then I'll attach a short video of what it does, which is not at all what is expected.