How Rs232 Commands Work - Clarity SN-4215-P User Manual

4.1 How RS232 Commands Work

The displays can be completely controlled through RS232 commands. These commands have a strict
protocol (format), which is described here. The list of commands is given in the Reference section.
With RS232 commands, you can do everything
you can do with the remote control and more.
(However, you cannot set the Group and Unit
ID numbers.) There are lots of "rules" about
RS232 commands:
• Transmission speed: 9600 baud
• 8 bits, 1 stop bit, no parity
• No standard hardware or software pacing
is used, such as DTR/RTS or XON/XOFF.
Commands should be paced by timing
by using the ACK, NAK, UNK, or ERR
responses from individual displays.
• Standard RS232 levels of +/ 12V are
used. Some laptops use ground (earth) and
+5V. These are not always successful in
communicating with the display.
• The display's RS232 port is always active,
except during the boot-up process, which
is the first 5 seconds after power is ap-
plied.
• The protocol for communication is a
7-byte command line:
STX IDT
1 byte 2 bytes
✎
Note: Time from STX to ETX must be less than 1
sec.
= Start of transmission = 02h
STX
Abbreviation Hex Decimal Character
STX 02
= Monitor Identification
IDT
This is used to identify which unit will
execute the RS232 command. The address is
divided into a Group Address (1
nd
Address (2 byte). There are four possible
address forms:
4 - 2
CMD ETX
3 bytes 1 byte
Control
2 Ctrl-C
st
byte) and Unit
• Single address: The whole address is
specified, such as 00, 01, A3, FF. Only
the single display that matches this
address attempts to execute this
command, and an ACKnowledgment is
sent.
✎
Note: In single address mode, the host computer
should wait for an ACK, NAK, UNK or ERR
response before sending the next command.
or
✎
Note: If several displays have the same Group and
Unit address and they receive a command to
their common single address, they will all
respond to the command, causing confusion
on the RS232 data line.
• Group address: The group part of the
address is specified, the unit part is
not, such as 1*, 9*, A*, E*. (A * is a
wildcard in the address.) All displays
which have the group number attempt
to execute the command, but no
acknowledgment is sent.
• Unit address: The unit part is
specified, the group part is not, such as
*2, *9, *D. All displays matching the
unit number attempt to execute this
command, but no acknowledgment is
sent.
• Broadcast address: Neither group nor
unit is specified, so the IDT part of the
command is **. All displays attempt to
execute the command, and no acknow-
ledgments are sent.
✎
Note: When global commands are sent (whenever
there is a * in the address) no reply is
returned from the display. Use a ½ second
delay between commands. This will avoid
the problem of a new command being sent
before the execution of the previous
command completes.