6 Commands
69
The 8 bit ASCII mode allows to transmit all characters from 0 to 255 (8 bit), inclusive the
IBM special characters. Defined special characters (e.g. Idle, CANGEOVER characters,
etc). can be transmitted using the Ctrl-character (refer to chapter 6.26, page 55)
In the Huffman mode only the ASCII characters 0... 127 (7 bit) can be transmitted. To
transfer certain IBM special characters (umlauts), the PTC converts these characters
according to the following table:
Umlaut ASCII Transmitted
Character
ä 132 14
ö 148 15
ü 129 16
Ä 142 20
Ö 153 21
Ü 154 22
ß 225 23
Table 6.2: Conversion of German special characters.
The Huffman data compression, which can improve speed up to 80% (effective character
length 4.5 to 5 bit) allows to reduce the middle character length. The data compression of
lowercase letters is better as for uppercase letters. The ASCII mode will be useful only if
the text contains non ASCII characters, or many uppercase letters.
The PTC firmware scans through each packet determining whether HUFFMAN or ASCII
coding will be more efficient for transmission, and selects the better one. Manually
selecting the ASCII mode (MOde 0) makes the controller transmit ASCII anyway. Doing
this should only be necessary in very special cases.
Automatic mode also works on characters exceeding 127 decimal. Therefore 7PLUS files
may be transferred without any user intervention.
The parameter 2 is effective only with a PACTOR Level II link. With Level I contacts,
the system behaves as if the parameter 1 had been chosen. The automatic compression
used in PACTOR-2 has proved to be very advantageous and reliable. Therefore, the
MOde parameter should only need to be changed in exceptional circumstances (e.g.
measuring the text throughput without compression) to a value < 2. There are no
problems caused by leaving the Level II compression turned on, even when transmitting
7Plus, binary files or graphics. No manual intervention by the operator is required, as the
PTC-IIIusb will switch automatically to uncompressed ASCII transmission for individual
packets, if necessary.
6.61 MONitor
This command switches to AMTOR listen mode (Mode L). In AMTOR listen mode, an
existing AMTOR ARQ link between two stations can be read on screen.
As the AMTOR listen mode requires a lot of computer time, it is not possible to receive
any FEC transmissions or answer PACTOR or AMTOR connect requests in this mode!
The PTC doesn’t react on PACTOR or AMTOR ARQ connect requests.
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