(
The PT automatically sets and confirms the checksum but the host computer
must be programmed to handle these tasks.
Checksum Calculation The checksum is the two’s compliment (2-digit hexadecimal) of the sum of the
code from the [ESC] code (1BH) at the start ofthe commandup to the checksum
at the end of the command.
Example
In the case where screen #762 (hexadecimal: 02FAH) is specified with the
Screen# Specify Transfer command [ESC] s.
[ESC] s 02FA SUM
Check sum
Check sum calculated from this code
As the commands are sent as character codes the checksum is calculated as
follows:
73
+30+32+46+41= 15CH
s02FA
The two’s compliment is calculated from the least-significant two digits (by sub-
traction from 100H), as follows:
100H -- 5CH = A4H
The command must appear as follows when it is sent by the program:
PRINT #1,CHR$ (&H1B);”s02FA”;”A4”
4-4 Precautions
Some important points to consider when using commands are listed below.
Command Length If a mistake during command specification results in a command being too long,
the correct length of the command is executed and the remainder is ignored.
A timeout error results if a mistake during command specification results in a
command being too short.
As a small numberofbytes is transmitted by the host, the interval betweentrans-
missions should not exceed 5 seconds if a command is divided up for transmis-
sion. A timeout error occurs if the interval between transmissions exceeds 5 se-
conds.
Whencommands are sent toofrequently, abuffer overflowerror may occurifthe
PT cannot keep up with the command processing.
The interval between command transmissions should not exceed 60 seconds
using the Online Transfer command. A timeout error occurs and operation re-
verts to Run mode if the interval between transmissions exceeds 60 seconds.
Control of the PT status by the operating commands is restricted by the PT
memory switch settings as listed below.
Operating command Restriction from memory switch
setting
Buzzer control command [ESC] T Effective when buzzer turned on
Alarm Output control command [ESC] ^ Effective when alarm turned on
The entire command is ignored if any point specified at coordinates X, Y with the
Terminal commands lies outside the screen.
Note If the PT’s SW1-1 is set OFF (automatic reset after communication error) no
message is displayed when a communication error occurs.
Interval Between
Transmitted Commands
Controlling PT Status with
Operating Commands
Coordinate Specification
with the Terminal
Commands
$
Section 4-4
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