HEIDENHAIN TNC 306 Technical Manual - Manual (Page 170)

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TNC 406/TNC 306 4 Gap control 3/97
4.9.2 Transmission from the PLC to the generator control
It becomes necessary for the PLC to transmit to the generator control when, for example, M36 is
output, a generator setting must be changed during erosion, or the operating mode of the control
must be changed.
For transmission the PLC provides Words W760 and W762, which must be loaded with the first
byte to be transmitted or with the number of the bytes to be transmitted. Strobe marker M2799
starts data transmission. If transmission is successful, ACK is transmitted to the PLC and the strobe
marker M2799 is reset. Marker M2799 must be reset before a new transmission can be started.
Data is transmitted according to the following protocol:
PLC transmits: <SYNC> <Number n > <ID character> <Hi-byte no.> <Low-byte no.>
<Byte 1> < > <....> <Byte n > <BCC>
Generator transmits: ACK/NAK
If the NC recognizes an error during data transmission, it sets one of the markers from Marker
M2924 to M2928. These markers from the memory area of the PLC error messages are
permanently reserved for displaying the transmission error and must not be used for any other
purpose. Markers M2930 to M3023 can be changed as desired.
If the generator control transmits NAK (faulty transmission) to the PLC, the data will be transmitted
two more times. If the generator control transmits NAK three times, the transmission is aborted and
Marker M2924 for "transmission error" is set.
Marker Function Set Reset
M2799 Strobe marker for starting transmission
to the generator control PLC NC
M2924 Transmission error (after three NAKs ) NC NC
M2925 False marker numbers NC NC
M2926 Address exceeds memory area NC NC
M2927 Generator setting missing NC NC
M2928 External unit is not ready NC NC
W760 No. of the first byte to be transmitted PLC PLC
W762 Number of bytes to be transmitted PLC PLC