Matrix Orbital Corp

Hello. New to the forum so welcome to me . My questions are regarding VK204-25, refering to manual version 2.0.

Section 2.4 General Purpose Outputs
The outputs appear on a 14-pin header but there is no schematic representation of the typical wiring for an output device.

Are all of the inside row of pins connected to ground?

Therefore the output is taken from the output pin with respect to ground, correct?

Therefore an output when turned ON presents 5V @ 20mA between the output pin and ground, correct?

Section 7.2 General Purpose Output Off command
The command format is shown as 0xFE 0x56 [Num] where [Num] refers to the desired GP output.

What is the format of the [Num] parameter? Does 0x00 correspond to GP output #1? Or perhaps 0x01? Or maybe yet 0x31 (ASCII for 1)? The point is that in embedded products like your displays, any of the above choices are possible. The programmer who developed the interface protocol decided which, but your documentation doesn't elaborate.

Manual sections in general
In the command descriptions there are fields such as [column] and [length]. Like the above [Num] field for GP output, these fields need better description as to valid values, ranges, number formats and what the numbers mean.

Section 9.4 Poll Key Press
This section discusses polling key presses but makes its statements in the context of an RS232 interface.

Does this mean that this particular command is NOT available if the I2C interface is being used for communication?

From what I've gathered from other threads on your forums I've concluded that a simple I2C read of the display will return one of the following:
1. Key code, represented by alpha character ("A" for R1C1, etc.)
2. Key code with top bit set indicating more characters are available in the key buffer. (There seems to be some disagreement on whether the top bit actually gets set, given some debate in other threads. Please comment)
3. 0x00 indicating no keys have been pressed
If my conclusion is correct then this command is meaningless in the context of I2C, correct?
If so then the question that begs to be asked is what happens if I do send it via I2C?
Same question for the Auto Transmit Key Presses On/ Off commands?
Does the key buffer still indicate both key down and key up codes?

In general therefore it seems the entire section on command interface could use some work regarding behavioral differences between the RS232 interface and I2C. RS232 is full duplex so the notion of the display asynchronously "pushing" data or auto-transmitting is valid. I2C however requires a master to operate the bus and one or more slaves to respond accordingly, suggesting a a "poll only" capability.

May I respectfully suggest that this section of the manual get revised to explicitly document each command in the context of RS232 vs. I2C, noting differences, irrelevances and exclusions where needed? May I also suggest that some example schematics of keyboard and GP output interface would go a long way in helping the many who have already asked questions about relay interfaces, voltages, currents, connection pin outs, etc., including myself .

As an aside I notice that President Henry has made some nice attempts to provide some references in the Guides forum which answer in part my above request for example schematics. However, the images links seem broken on many of the threads. Just an FYI.

Thanks in advance.

Hello Steve,

Thanks for your post.
As much as we want to clarify and elaborate the manual, we still fall short of people's expectations. Thanks for pointing them out, they are now being considered for manual updating.

Are all of the inside row of pins connected to ground?
Therefore the output is taken from the output pin with respect to ground, correct?
Therefore an output when turned ON presents 5V @ 20mA between the output pin and ground, correct?

Yes to all 3 questions.

Section 7.2 General Purpose Output Off command
The command format is shown as 0xFE 0x56 [Num] where [Num] refers to the desired GP output.

What is the format of the [Num] parameter? Does 0x00 correspond to GP output #1? Or perhaps 0x01? Or maybe yet 0x31 (ASCII for 1)? The point is that in embedded products like your displays, any of the above choices are possible. The programmer who developed the interface protocol decided which, but your documentation doesn't elaborate.

ALL of the parameters are in decimal format. In the VK204-25, there are 6 GPOs. Therefore [Num] can only be valid for 1 - 6. We expect the decimal values of 1-6, not ASCII. So for eg. to turn GPO # 5 off, one need to send: 254 / 86 / 5.

Manual sections in general
In the command descriptions there are fields such as [column] and [length]. Like the above [Num] field for GP output, these fields need better description as to valid values, ranges, number formats and what the numbers mean.

The vaild input of these parameters depend on the size of the display. In the case of a VK204-25, column is 1 - 20, row is 1 - 4.

Section 9.4 Poll Key Press
This section discusses polling key presses but makes its statements in the context of an RS232 interface.

Does this mean that this particular command is NOT available if the I2C interface is being used for communication?

This command is not advisable (though can be used) in I2C because the read of the keys are done by simply sending the read address of the slave, no need to send the command. We are working on newer manuals that mentions if the command is not available in I2C, otherwise it is.

From what I've gathered from other threads on your forums I've concluded that a simple I2C read of the display will return one of the following:
1. Key code, represented by alpha character ("A" for R1C1, etc.)
2. Key code with top bit set indicating more characters are available in the key buffer. (There seems to be some disagreement on whether the top bit actually gets set, given some debate in other threads. Please comment)
3. 0x00 indicating no keys have been pressed
If my conclusion is correct then this command is meaningless in the context of I2C, correct?
If so then the question that begs to be asked is what happens if I do send it via I2C?
Same question for the Auto Transmit Key Presses On/ Off commands?
Does the key buffer still indicate both key down and key up codes?

1, 2, 3 Yes to all these.
This is why Poll Key Press is meaningless in I2C. If you send the Poll Key Press command, you will have to follow it with a read of the display, and therefore get the same result thus making Poll Key Press meaningless in I2C. Same goes for Auto Transmit On/Off. You are getting the gist. The buffer can indicate the key down / key up code in I2C mode.

Again, we have started a newer manual that indicates when a command is not available in I2C, because most of the time they are. Please bare with us as we finish up the newer manuals and get back to the old ones (such as the VK204-25) after.

Thanks,

Raquel,

You've very eloquently answered all of my questions. Thank you so much.

I can certainly be patient regarding manual updates as I understand completely the issues involved. I just wanted to provide you with some (hopefully constructive) feedback.

I've visited many different forums for products I've used in my career and I must say this one is the most professional I've run across. You and your staff members conduct themselves professionally and helpfully. Please know it is appreciated.

If I have any more questions I certainly know where to go for great and helpful answers.

Hello Steve,

Thanks very much for the kind words. I am sure this is appreciated by all of us here at MO.

Best Regards,