2019r0
Page 40 of 82
Mercury 2+ Operator Terminal User Manual
The block format for messages in multidrop are similar to that for
PointtoPoint mode, and are received as well as transmitted:
<STX> ADDR FUNC ID DATA DMY CSUM <ETX>
These fields are described on page 38. The following fields have
additional options in multidrop mode as follows:
Block Format
Mercury 2+ Terminal can be set to respond to any
address in range 1 to 15 in the Setup menu. Address 00
is reserved for broadcast to all slave terminals.
In addition to the codes B, C and E described in Point
toPoint Mode, a single byte defines the block source as
follows:
"A" (41
H
) block from operator keyboard entry
"D" (44
H
) block from keyboard function key (Fl to F8)
Format differs slightly for sending or receiving data
blocks. Block data received by the Mercury 2+ can be
up to 128 bytes long, containing visible characters and
escape sequences.
Block data transmitted by the Mercury 2+ includes one
of the above ID bytes or the "Multidrop Acknowledge"
block (see Setup menu on page 25). No acknowledge
ment is sent if the received block was a broadcast.
ADDR
ID
DATA
A key or series of keys pressed on the terminal are stored into an
output buffer on the key press ENTER. The master unit reads the
output buffer on a FIRSTIN, FIRSTOUT basis. The escape
sequence to send the next buffer is defined in Table 6 on page 34.
Examples of typical sequences and how they are composed are
given in Appendix B.
Sending Block
