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The function of bits in C are shown in the following diagram and explained in
more detail below.
15 14 13 12 11 00
Number of items in range (N, BCD)
001 to 999 words or bytes
First byte (when bit 13 is ON)
1 (ON): Rightmost
0 (OFF): Leftmost
Calculation units
1 (ON): Bytes
0 (OFF): Words
C:
Not used. Set to zero.
Number of Items in Range The number of items within the range (N) is contained in the 3 rightmost digits of
C, which must be BCD between 001 and 999.
Calculation Units The frame checksum of words will be calculated if bit 13 is OFF and the frame
checksum of bytes will be calculated if bit 13 is ON.
If bytes are specified, the range can begin with the leftmost or rightmost byte of
R
1
. The leftmost byte of R
1
will not be included if bit 12 is ON.
MSB LSB
R
1
12
R
1
+1 3 4
R
1
+2 5 6
R
1
+3 7 8
When bit 12 is OFF the bytes will be ORed in this order: 1, 2, 3, 4, ....
When bit 12 is ON the bytes will be ORed in this order: 2, 3, 4, 5, ....
Conversion to ASCII The byte frame checksum calculation yields a 2-digit hexadecimal value which is
converted to its 4-digit ASCII equivalent. The word frame checksum calculation
yields a 4-digit hexadecimal value which is converted to its 8-digit ASCII equiva-
lent, as shown below.
3 4 4 1
Byte frame checksum value
D
4A
4 6 3 1
Word frame checksum value
D+1
F10B
3 0 4 2
D
Flags ER: Indirectly addressed DM word is non-existent. (Content of DM word is
not BCD, or the DM area boundary has been exceeded.)
The number of items is not 001 to 999 BCD.
The calculation range exceeds the data area.
Special Instructions Section 5-25