Mercury 2+, Руководство пользователя

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2019r0 Page 52 of 82 Mercury 2+ Operator Terminal User Manual
Checksum
Calculation
To calculate the CSUM for the above example:­
Take the Hex value of the Characters and add them all together.
The codes are listed on page 31.
<STX> (02
H
)
ADDR 01 (30, 31
H
)
FUNC R (52
H
)
DATA TEST (54,45,53,54
H
)
DMY <NUL> (00
H
)
Sum of above codes:­
02+30+31+52+54+45+53+54+00 = 01F5
H
01F5 in Hex = 111110101 in Binary
'AND' the above with (7F
H
) = 1110101
Negate the above (two's complement) by inverting all bits
and add 1 = 0001011 = 0B
H
This value is less than 20
H
, which is a control code and so the
process needs to be repeated with DMY = 20
H
. This results in a
new checksum having the value 6B
H
, which translates to the
character "k".
To transmit the word "TEST" to the terminal at address 01, the
following string needs to be sent:­
"<STX> 0 1 R T E S T <SP> k <ETX>"
Using the format described above, the Master sends a block to read
the output buffer on a Mercury 2+ terminal with Multi­drop
address 01 as follows:­
<STX> (02
H
)
ADDR 01 (30,31
H
)
FUNC R (52
H
)
DATA "<ESC> [ ? 9 ; 1 z" (1B,5B,3F,39,3B,31,7A
H
)
DMY <NUL> (00
H
)
The checksum can be calculated to be 77
H
, which is the ASCII
code for the letter "w".
The block to be sent to the terminal takes the form:­
"<STX> 0 1 R <ESC> [ ? 9 ; 1 z <NUL> w <ETX>"
The Re­send Last Block command (see page 34) allows the buffer
to be read repeatedly.
Reading the
Block Buffer