8 data interface – HEIDENHAIN TNC 407 (243 020) Technical Manual User Manual
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4.8 Data Interface
The following modules enable the PLC to transfer data across the V.24/RS-232-C or V.11/RS-422
data interfaces.
(For transfer parameters see chapter entitled "Data Interface")
The PLC assigns and enables the interfaces with Modules 9100 and 9101 respectively; the current
status of the data interface can be interrogated with Module 9102.
The transmit and receive buffers for the PLC are 128 characters long. Since every STRING ends with
an END character a STRING in the transmit or receive buffer can only be up to 127 characters long.
As well as transmitting and receiving a STRING from the STRING memory (Modules 9103 and
9104), Modules 9105 and 9106 can be used to transfer a block of binary values (bytes) from the
Word memory.
However ASCII characters are transmitted and received across the interface in both instances
(STRING and binary transmission).
Example: Transferring a binary block
11111010
➞ B126
.
.
.
10000001
= $ FA
= $ 81
.
.
.
.
When transferring binary data from the Word memory from address B126 the ASCII characters "F",
"A", "8", "1" etc. are transmitted consecutively across the interface.
Since each byte contains two ASCII characters when transferring binary data, the transmit and
receive buffers are 63 bytes long.
With the help of Module 9107, when transferring binary data, each byte (two ASCII characters) can
be read from the receive buffer without the buffer being erased.