The 8255 io Reading & Servo Rotation Problem

8255 IIB
The 8255 issues have not been settled yet. Since last week we are having difficulties in finding what's the real problem that hinders the input port from being read.

What happened now is that, any input from Control Register 1 and 2 whether port A,B or C, all display 0xff. This is incorrect since the program have not been altered. Last time any point can be read. I guess there could be some hardware problem with that old board, but for the time being I can't prove it yet.

Today, I tried the second control register and double the 8255 Intermediate Interface Board (IIB) wiring to ensure my test wiring is OK. Unfortunately, even with correct wiring, same old working problem, still the reading from the input port come out 0xFF.

This is really frustrating since the program I use to test is the actual working program. Next, it slow down the project progress. What more, as I can't proceed with the USB project yet as long as this issue is not solved.


Servo Rotation
This is the prototype circuit assembly that I used to signal the Servo Motor movement. As you can see there are two variables resistors, one for timing range(limit-1Mohm) and another one(500kohm) to move the servo. I collect some information regarding Servo Motor characteristics that might help in solving the rotation issue with my parallax Futaba S3003. It says that for most standard SM specs that timing for neutral position is about 1.5ms. Any timing longer than 1.5ms will force the SM to turn CW, and vice versa. Usually the timing range is between 1 to 2 ms. From one sets of timing signal, the minimum delay is about 20 to 30ms is required to protect the gear of the SM. With some modification the SM turning degrees can be adjusted up to user requirement. Even for some cases, it is possible to modify up to basic DC motor.

Due to this features of the SM, so the conclusion for my SM problems can only be conclude once I managed to come out with perfect timing with correct equipment such as oscilloscope.