Nuts and Volts - November 2008

put the keypad matrix system into Key Up/Down Mode. In this mode, the panel does not send characters continually while the key is depressed. Instead, it senses a key press and immediately sends the character associated with the key. No other characters will be transmitted until the key that is being depressed is released. Here’s the command code to put in for Key Up/Down Mode:

printf(“%c%c%c”,0xFE,0x7E,0x01);

LOST IN THE WOODS AT NIGHT IN THE RAIN

It’s obvious that the GLK240128-25 is designed to be easy to deploy. I had absolutely no problems with the hardware or the MOGD# application. However, I did run into a gotcha with the RS-232 interface.

My initial PIC hardware design was driven by a 20 MHz ceramic oscillator. The PIC18F2620 showed no signs of any abnormality and its EUSART did not exhibit any problems when communicating with my Tera Term Pro emulator. However, I could not communicate with the GLK240128-25 RS-232 port reliably at any of its supported baud rates. I figured I had a bogus unit. I happened to have two of them and swapping in a new unit didn’t change a thing. So, I placed a call to Matrix Orbital’s support center and began a problem-solving conversation with Troy Clark. Troy was very supportive and was always available to take my calls.

After several days of emails and phone calls to Troy, I narrowed the problem down to the ceramic oscillator that I was using to clock the PIC18F2620. There was absolutely no science or logic associated with finding the root cause of the problem. I stumbled into the fix. In complete desperation, I replaced the 20 MHz ceramic oscillator with a 20 MHz crystal and the panel never lost another

THE DESIGN CYCLE

SOURCES

Matrix Orbital — www.matrixorbital.com Matrix Orbital GLK240128-25; MOGD#

HI-TECH Software — www.htsoft.com HI-TECH PICC- 18 PRO

Microchip — www.microchip.com PIC18F2620; MPLAB IDE

character when communicating with the PIC18F2620. I won’t disparage the ceramic oscillator manufacturer here as my problem may be an isolated incident. Needless to say, I trashed my stock of that manufacturer’s ceramic oscillator devices.

WRAP-UP

You have been exposed to a pair of methods (sendchar and printf) that allow you to exploit the full feature set of the Matrix Orbital GLK240128-25. The sendchar method is more suited for smaller applications that are being driven by PIC microcontrollers with limited memory resources. PIC microcontrollers with larger program memory areas can take advantage of the printf command method.

We’ve only scratched the surface of this panel’s capabilities. Reading about what it can do does not do this LCD panel justice. I’ve given you a firmware jump start on putting one to work. To get a feel for how versatile the GLK240128-25 really is, you’ll just have to get a one of your own and meld it into your Design Cycle. NV