8 – 16 HEIDENHAIN Technical Manual TNC 426, TNC 430
8.3.3 Configuration of Interfaces
To configure data format and the type of handshake in the EXT1/EXT2/EXT3
operating modes (EXT3 only for the PLC):
7
77
7 Select machine parameter MP5020.x.
Data bits With bit 0 you determine whether transmission is to be with seven or eight
data bits. Transmission with seven bits is normally used, for printer interfacing
eight bits are required.
Block Check
Character (BCC)
With bit 1 you can ensure that the BCC is not interpreted as a control
character.
On the TNC, numbers less than $20 are defined as control characters. If
calculation of the BCC produces a number less than $20, then a blank space
is sent in addition immediately before <ETB>. The BCC will consequently
always be greater than $20 and therefore cannot be interpreted as a control
character.
Hardware
handshaking
With bit 2 you can determine whether the TNC stops transfer from an
external device by sending an RTS signal.
n Data output from TNC to EXT
When the receiving buffer is full, the external device resets the RTS signal.
The TNC detects that the peripheral unit receiving buffer is full at its CTS
input:
C
T
R
T
RxD
TxD
RST
CST
TxD
RxD
+
TNC
+
+
+
+
+
+
+
EXT
Activating
data output
Input buffer
full
Data
+ positive voltage level
negative voltage level
Data Data
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