Owner manual

8.3 RS232 interfaces
746 VA Trace Analyzer / 747 VA Stand
8-11
8.3.2 Data transmission protocols
In the 746 VA Trace Analyzer, methods and determinations are stored as a file in
binary compressed form. Such binary files can be transferred via the RS232 in-
terfaces and also be read back in. The binary data are transferred with a block-
oriented protocol. The blocks, comprising 128 data bytes and 5 control characters,
have the following structure:
Block head
1 Byte
Block number
1 Byte
Useful data
128 Byte
CRC
1
st
Byte
CRC
2
nd
Byte
CRC = Cyclical Redundancy Check following CCITT V.41
The control characters SOH (any block), EOT (last block) and CAN (premature
abort) can be used a block head. For the transfer of binary files between the 746 VA
Trace Analyzer and a PC, the two Windows PC programs 6.6017.000 Metrodata
VA Back Up and 6.6016.103 Metrodata VA Database are available.
In the output of ASCII reports (e.g. Full report) to the RS232 interfaces, strings
of up to 82 ASCII characters incl. data delimiters (CR or LF) are transferred. If no
printer is attached (Printer = none), an ETX with CR/LF is sent at the end of each
such text block and an EOT with CR/LF at the end of a transfer.
In addition to the output of normal ASCII reports, the 746 VA Trace Analyzer also
offers the possibility of transferring the two special reports ActDetm and ActMeth
comprising a binary file (determination or method) and an ASCII report. The two
Windows PC programs 6.6017.000 Metrodata VA Back Up and 6.6016.103 Met-
rodata VA Database are available for the receipt and further processing of these
reports.
8.3.3 Settings and modes
The two RS232 interfaces are set as follows when first initialized:
Baud rate 9600
Data bits 8
Stop bit(s) 1
Parity none
Handshake HWshort
Receive mode off
If characters are nonetheless received in this default setting with the receive mode
switched off, these are read individually and discarded. This prevents the external
device blocking the transmission process of the 746 VA Trace Analyzer by sending
characters.
The internal mode of the RS232 interfaces is switched automatically, depending on
the type of transfer (see section 8.3.2). This concerns both the receive abort criteria
and the partition of the buffer. The following modes are possible:
• Receive balance data
The buffer of the RS232 interface is divided into 82 characters for receive and
82 characters for send. The receive buffer is emptied following the delimiter
character LF. Otherwise, the RS232 parameters set on the dialog page ”VA
TRACE ANALYZER” apply.