. 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.
