2.3 Text Packet Format
Each text packet contains the following information and is structured as shown below:
[STX] [No. Bytes] [Command] [Data] [Checksum] [ETX]
NOTE:
EOT
(
0x04
),
ENQ
(
0x05
),
ACK
(
0x06
), and
NAK
(
0x15
), and are single-byte control characters, with
nothing else added to them.
2.3.1 STX
Every text packet begins with this Start of Text control character (hexadecimal
0x02
or CTRL+B), except as noted
below.
NOTE:
The Start of Text control character (
STX
/
0x02
) is
not
added when sending
ENQ
(
0x05
),
ACK
(
0x06
),
EOT
(
0x04
), or
NAK
(
0x15
) because these are single-byte control characters, not text.
2.3.2 No. Bytes
The No. Bytes (Number of Bytes) part of the text packet is the number of characters in the Command and Data parts
of the packet. This value is expressed as a 2-digit hexadecimal with its characters encoded as ASCII.
EXAMPLES:
• If Command is four characters and Data is six characters, the No. Bytes decimal value is 10. In the text packet,
No. Bytes will be
0x0A
in hexadecimal, so the ASCII character value for No. Bytes will be
0A
. This is encoded in
ASCII as
0x30
,
0x41
.
• If the number of Command plus Data characters is 16, No. Bytes will be
0x10
in hexadecimal, so the ASCII
character value for No. Bytes will be
10
, which is encoded as
0x31
,
0x30
.
2.3.3 Command
The Command part of the text packet is next. The list of available Commands is contained in “RS-232 Commands”
on page 50. A Command is up to four characters long. If a Command does not contain four characters, the
remaining characters must be the ASCII space character (
0x20
). The Command is transmitted as ASCII characters.
2.3.4 Data
The Data part of the text packet is after the Command. The Data part can be from 0 to 251 characters long,
depending on the Command. The Data part is transmitted as ASCII characters, typically a decimal representation of
a number.
Appendix B — RS‑232 Protocol (continued)
Ultimus V High Precision Fluid Dispenser
43
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