Holtek HT-IDE, Руководство пользователя

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get_column: ;calculate column number
mov a,temp ;load temp
xor a,mask ;test column number
snz z ;
jmp index ;no. test next column
ret ;yes. return (TBLP)
index: ;next column
inc tblp ;(9) ;table index+1
set c ;
rlc mask ;shift mask left (LSB=1)
jmp get_column ;repeat get_column key_in endp
delays proc ;delay subroutine
mov a,0ffh ;load counter
mov count1,a ;
d1:
sdz count1 ;count down count1
jmp d1
ret
delays endp
org 300h ;display data table
dc 0fh,0eh,0dh,0ch ;key0, key1, key2, key3
dc 0bh,0ah,09h,08h ;key4, key5, key6, key7
dc 07h,06h,05h,04h ;key8, key9, keyA, keyB
dc 03h,02h,01h,00h ;keyC, keyD, keyE, keyF
end
Program description
Section (1) defines whether the port bits are defined as inputs or outputs.
The program enters a loop to determine which key is pressed. The code
works by first scanning line by line to determine if any key has been pressed
in that line. Because four keys are connected together in the same line, the
software must determine the exact key, which has been pressed. For
example in section (2) the first line is scanned to see if key 0~3 has been
pressed. If so this code then jumps out of this scanning loop to a subsection
(3), to determine which key connected to this line has been pressed. If not
the code moves on to look at the line containing keys 4-7 and so on. After
entering this code subsection, the code first stores the key value in a
temporary register as shown in section (4). There then follows a short time
delay (5), to take account of switch bounce and then code to determine when
the switch has been released (6). The code will not continue until the key
has been released. The next part is to determine which row has been
pressed (7). When jumping from row to row the corresponding table address
jumps by 4 bits each time (8). After determining the row, the pressed key
connected to this row has to be found. To do this the value in the accumu-
lator jumps in increments of one bit until the correct key is located, as
shown in (9). The correct key has thus been found by first looking at the
Chapter 15 Input/Output Applications
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