Help on interpreting a serial protocol.
Renato Mendes
I have a requirement for a system that needs to be interfaced to a PC using
serial lines. These serial lines has no standard as they were made for a
special purpose equipment. I'll try to describe how my system architecture
is and how the serial line and protocol works, followed by some questions.
My architecture is as follows:
SYSTEM1 --------<Serial Line 1>------------ SYSTEM2
|
|------ PC Connected
SYSTEM3 --------<Serial Line 2>------------ SYSTEM4
|
|------ PC Connected
As seem above, I have a serial line connecting SYSTEM1 to SYSTEM2 and
another connecting SYSTEM3 and SYSTEM4. I'll have to connect in parallel a
PC with a serial board just to acquire the data that's being exchanged
between both pair of systems for analisys. I don't need today to send
messages, but only to acquire and interpret what's going on in the serial
lines.
The pairs SYSTEM1/SYSTEM2 and SYSTEM3/SYSTEM4 do not interact with each
other, but they're not similar. Serial Line 1 is different from Serial Line
2.
My electrical specifications are:
Serial Line 1: 20mA current loop
Serial Line 2: 0-5V (0V = MARK, 5V = SPACE)
The protocol that's exchanged between both systems is BIT ORIENTED, detailed
below:
Baud Rate: 1200bps or 2400bps
The protocol, bit oriented, has 4 start bits (all "1"), followed by 2 words
of data then 2 CRC's, followed by 18 stop bits (all "0"). On every 8 bits
from the start bits its set to "1" for synchronism.
So, it looks like:
<idle>1111ddddddd1ddddddd1ccccccc1ccccccc1000000000000000000<idle>
Where: ddddddd is data words
ccccccc are CRC words.
<idle> is the time where the line is idle
My purpose is to receive both data packets from the message in a continuous
mode (like an serial line analyzer), running on a PC equipped with some sort
of serial intelligent board.
I would like to know where may I find a serial board that will fully attend
this necessities ? The board must accept such configuration (4 start "1"
bits, 7 data bits mixed in the message, 18 stop "0" bits, etc).
Probably the board is programmable in C so that I can program my protocol
and download it to it. The operational system requirement is Windows-NT.
Thanks in advance for any kind of help.
Regards,
Renato Mendes
////////////////////////////////////////////////////////////
Renato Mendes
renato...@contrastenet.com.br
Contraste Engenharia e Automação Ltda.
www.contrastenet.com.br
