The Microcontroller Idea Book - Jan Axelson's Lakeview Research

Switches and Keypads
Listing 7-3. Test program for Figure 7-9’s circuits.
10 XBY(1F00H)=49 : REM 1
11 XBY(1F01H)=50 : REM 2
12 XBY(1F02H)=51 : REM 3
13 XBY(1F03H)=67 : REM C
14 XBY(1F04H)=52 : REM 4
15 XBY(1F05H)=53 : REM 5
16 XBY(1F06H)=54 : REM 6
17 XBY(1F07H)=68 : REM D
18 XBY(1F08H)=55 : REM 7
19 XBY(1F09H)=56 : REM 8
20 XBY(1F0AH)=57 : REM 9
21 XBY(1F0BH)=69 : REM E
22 XBY(1F0CH)=65 : REM A
23 XBY(1F0DH)=48 : REM 0
24 XBY(1F0EH)=66 : REM B
25 XBY(1F0FH)=70 : REM F
30 DO
40 ONEX1 100
50 WHILE 1=1
60 END
100 KEY=XBY(0E000H).AND.0FH
110 DAT=XBY(1F00H+KEY)
120 PRINT CHR(DAT)
130 RETI
requested function. Chapter 8 describes how to add a small display to a system, so you don’t
have to use the host computer’s display for the menu.
For some projects, you may want to use the numeric values of the keys directly, rather than
interpreting them as ASCII codes. In this case, you’ll need to revise the lookup table, or
create a second table that matches the numeric values of the key legends with their data
outputs. For example, a data output of 0 would correspond to 1, instead of 49 (the ASCII
code for 1). Again, you usually can’t use the keypad encoder’s data outputs directly because
they don’t correspond to the values printed on the keys.
If an application requires that users enter multi-digit numbers on the keypad, your program
will have to translate the individual digits into a single value. Listing 7-4 is a program that
waits for the user to enter a 4-digit hex address, then displays the data stored at that address
in external RAM.
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