HEIDENHAIN TNC 335 Technical Manual - Manual (Page 529)

8-22
TNC 360 2 TNC data interfaces 8/95
2.5 Configuration of the interface
2.5.1 Selection of the interface
The following settings can be selected with the appropriate data format and the data transmission
protocol.
In addition to the three freely configurable operating modes EXT, there are two fixed modes (ME
and FE). The FE mode must be set if the HEIDENHAIN floppy disk unit or an external computer
using the TNC.EXE transmission software is connected. In this mode, the transmission protocol with
Block Check Character is rigidly defined.
The ME operating mode matches the HEIDENHAIN ME 101/ME 102 magnetic tape unit and must
be selected if this is to be connected.
In this mode, the standard transmission protocol is set.
However, there is one important difference:
The character <EOT> is never sent because this character cannot be processed by the magnetic
tape unit.
2.5.2 Freely configurable interfaces
The operating mode EXT is freely configurable via the machine parameters.
The data format and the type of handshake are set in the MP 5020.
Data bits
Bit 0 can be set to determine whether transmission is to be with 7 or 8 data bits. Transmission with
7 bits is normally used, but 8 bits are needed, especially for printer interfacing.
BCC
If calculation of the BCC produces a number less than $20 (i.e. a control character) then a "Space"
character ($20) is sent in addition immediately before <ETB>. The BCC will consequently always be
greater than $20 and cannot therefore be recognized as a control character.