Mercury 2+, Руководство пользователя

Страница: 53 / 82

Mercury 2+ Operator Terminal User Manual Page 53 of 82 2019r0
Reading the
Digital Inputs
The Control Character String to read the Digital Inputs in Multi­
drop mode is:­
"<ESC> [ ? 4 z"
Using the method demonstrated above, the block to be sent in
multi­drop mode becomes:­
"<STX> 0 1 R <ESC> [ ? 4 z <NUL> h <ETX>"
This action causes the status of the external contacts to be copied
into the output buffer. It is possible to incorporate a Block Read
instruction into a single block command by putting into the DATA
field both the Control String to read the digital inputs and the
Control String to read the block buffer.
If the destination terminal is set up with Multi­drop Acknowledge
Enabled then the Mercury 2+ terminal sends an Acknowledge
Block back to the master. It does this on receipt of a valid Block of
matching address (i.e. the Multi­drop Protocol is correct) and takes
the form:­
"<STX> 0 1 D <NUL> Y <ETX>"
This string acknowledges that a message with the correct protocol,
ie FUNC, CSUM, etc. has been received, not that the message data
is recognised. So if a message is constructed with a non­existent
Escape sequence in DATA yet with the correct protocol, then a
Multi­drop Acknowledge is transmitted but the Mercury 2+
ignores the instruction.
When the Digital Inputs are read to the block, no information is
relayed back to the Master. If Multi­drop Acknowledge is enabled,
however, then the acknowledge would confirm that the message
was received correctly.
Multi-Drop
Acknowledge
Mode