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The Keyboard Ok, from memory, here is how the keyboard works (sorry if I'm telling you what you already know): As you know, the Alpha, Shift and ON keys have their own I/O pins. Thus they are easy to read directly. The rest of the keys are on their own matrix, which is the pretty standard way to do things. They are hooked up to port G (which has 16 pins). The matrix is configured wo there is a 'row' part, and a 'column' part. Pressing a key joins the corrosponding row line to the column line. The upper 8 port G pins control the column select, and the lower pins control the row data. The row data pins are configured as inputs, with pull-up resistors enabled. The idea is that if nothing is connected to the input, it will read '1'. By default, all row select lines are all grounded. This basically means that if no key is pressed, the row data pins will read 1111 1111 In this case, If a key is pressed, the column line (which is grounded) is connected to the row line. Hence the row reads 0. The following data shows what is read from port G when a key is pressed, starting from the HIST row and working downwards: FD - 1111 1101 - ' FB - 1111 1011 - SIN F7 - 1111 0111 - X EF - 1110 1111 - 8 DF - 1101 1111 - 5 BF - 1011 1111 - 2 7F - 0111 1111 - . So this method works fine for detecting what row a key is on. But, you also need to know the column. So what you do is make all the column select pins _inputs_ (so they are effectivly disconnected), except you ground the column select pin for the column you wish to test. Suppose you ground column select pin 2, and leave the rest floating (AKA inputs). No key pressed: 1111 1111 <-- row data all ones, as they are unless connected to ground key pressed on column 3, row 0 1111 1111 <- row data all 1's, since column 3 is connected to row 0, and column 3 is floating (you grounded column 2, remember) key pressed on column 2, row 4 1110 1111 <-- row data all 1's except for row 4 - since column 2 is connected to row 4. Column 2 is grounded, dragging row 4 to 0 Now, let look at the isKeyPressed() function int keyb_isKeyPressed(unsigned char col, unsigned char row) { //returns 1 if the key at logical column 'col', logical row 'row', is pressed //0 otherwise. unsigned int volatile * GPGDAT = (int*) 0x7A00064; //data unsigned int volatile * GPGCON = (int*) 0x7A00060; //control int volatile i=0; int keyPress = 0; if (!keyb_isAnyKeyPressed()) { return 0; //bail out right away if no key is pressed } unsigned int control = 1<<((col+8)*2); //set the correct col pin to output, others inputs control = control | 0xAAA9; //fix up the lower bits
- GPGCON = control; // write the new control value.
- GPGCON = 0x5555AAA9; //restore default
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Page last modified on October 20, 2004, at 06:10 AM