3 settings and modes – Metrohm 746 VA Trace Analyzer User Manual

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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

Byte

CRC

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

Stop bit(s)

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.