1.2.Keypad Subsystem
The keypad subsystem scans the key matrix, converts the scan code to its associated key value, and stores the value in the input buffer of keyboard for program utilization. Note that the [SHIFT] key is not stored into the buffer, it is used to distinguish the alphabetic and numeric mode of associated key position and provide an alternative key code. The following table shows the key values of each key.
Table of Key Values
Key | Value |
| Key | Value | Key | Value | Key | Value |
A | 41H | O |
| 4FH | [SP] | 20H | F1/? | 86H |
B | 42H | P |
| 50H | 0 | 30H | F2/?? | 87H |
C | 43H | Q |
| 51H | 1 | 31H | F3/? | 88H |
D | 44H | R |
| 52H | 2 | 32H | F4/? | 89H |
E | 45H | S |
| 53H | 3 | 33H | F5/* | 8AH |
F | 46H | T |
| 54H | 4 | 34H | F6/? | 8BH |
G | 47H | U |
| 55H | 5 | 35H | F7/? | 8CH |
H | 48H | V |
| 56H | 6 | 36H |
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I | 49H | W |
| 57H | 7 | 37H |
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J | 4AH | X |
| 58H | 8 | 38H |
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K | 4BH | Y |
| 59H | 9 | 39H |
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L | 4CH | Z |
| 5AH | [E] | 0DH |
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|
M | 4DH | + |
| 2BH | [C] | 08H |
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N | 4EH | - |
| 2DH | . | 2EH |
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1.3.Display Subsystem
This subsystem provides the interface functions: Display character, Display string, Set cursor position, and Clear screen display. The display coordinates are organized as follows:
Min Min Max Max
Row Col Row Col
0 0 1 15
The origin (0,0) is always at the upper left hand corner.