102 D50 PLC User's Manual
Instruction
Mnemonic Decoder and Encoder with 8421 Range
Bit
■ Byte
ENCO
DECO
ENCO: 8421 encoder
DECO: 8421 decoder
Word
Ladder
ENCO: Inspect the S register. If there is a bit in the On state, encode
it (on bit n) and store it in the low-order 8 bits of D. If there are two
or more bits in the S register that are in the On state, only the highest
bit will be processed. The higher 8 bits of D do not change.
DECO: Interpret the lower 4 bits of the S register and store in D.
Description
1. ENCO: Set D to the value of the bit number of highest bit in S that is On (0 to 16). If there are
two or more On bits in S, use the location of the highest bit. The high-order 8 bits of D do not
change.
2. DECO: Set the bit location (0 to 15) in D pointed to by the value in the low 4 bits of S. All
other bits in D are reset to 0.
ENCO $0000
→$00 $0020→$06 $0800→$0C
$0001
→$01 $0040→$07 $1000→$0D
$0002
→$02 $0080→$08 $2000→$0E
$0004
→$03 $0100→$09 $4000→$0F
$0008
→$04 $0200→$0A $8000→$10
$0010
→$05 $0400→$0B
DECO $0
→$0001 $6→$0040 $C→$1000
$1
→$0002 $7→$0080 $D→$2000
$2
→$0004 $8→$0100 $E→$4000
$3
→$0008 $9→$0200 $F→$8000
$4
→$0010 $A→$0400
$5
→$0020 $B→$0800
ENCO
D =
S =
R
R
DECO
D =
S =
15..8 7 6 5 4 3 2 1 0
S 0..0 0 1 1 1 0 0 0 0
D 0 0 0 0 0 1 1 1 6+1=7
invar
iable
ENCO
S ..... x x x x 0 1 0 1 = 5
D 0..0 0 0 1 0 0 0 0 0
15..8 7 6 5 4 3 2 1 0
DECO
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