USING THE NON-INTELLIGENT TERMINAL PROTOCOL
UNILINK HOST ADAPTER A-4
USER MANUAL
A.1.5 Error
-Checking Code
Following the message body is an ASCII four-character error-checking code
(ECC)
in the
form of a 16-bit hexadecimal number that is included at the end of
the message just before the semicolon terminator. The ECC is a checksum
computed
by both the sending and receiving stations as follows:
1. Divide the character count and the message body into blocks of four
characters, left-justified and zero-filled. The beginning and ending
delimiters
are not included in the calculation.
2. T
reat each block as a four
-digit hexadecimal number
.
3.
Sum the resulting numbers (blocks).
4. T
ake the two’
s complement of the sum to get the ECC.
As
an example, consider a message whose body is the CONFIGURE ADAPTER
command:
20
32 30
01
30 31
00
30 30
02
30 32
02
30 32
00
30 30
0E
30 45
ASCII
Codes
The total character
count
is found by adding together the number of characters
in the message, the four characters for the ECC, the four characters for the
character
count, and the two characters used to delimit the
message. Thus, the
total
character count for a message containing “2001000202000E” is
Starting Delimiter –
Character Count –
Message Body – 2001000202000
Error–checking Code
Ending Delimiter –
T
otal Character Count
* Numbers in parentheses are the corresponding
decimal values.
:
?
E
?
;
=
=
=
=
=
01
04
0E
04
01
(1)*
(4)
(14)
(4)
(1)
0018 (24)