Chapter 2
Multidrop Communications
2-4
MS-5000 Multidrop Concentrator User’s Manual
2-
M
ul
tidro
p Comm
.
the decoder still does not receive an ACK it will transmit a RES (reset)
and discard the data in its buffers.
• If the decoder transmits data to the concentrator and the concentrator
responds with an ACK or NAK, but the decoder doesn’t receive the con-
centrator’s response, the decoder will timeout and transmit a REQ to the
concentrator and request another response. If, after three retries (the num-
ber of times it transmits a REQ to the concentrator) the decoder receives no
response, it ends the transmission with a RES (reset).
1
Select Commands from the Host
Unlike poll requests,
select
commands always originate from the host and
consist of configuration or operation commands to decoders and other de-
vices that are configured in Multidrop. The decoder complies with the com-
mand when it is polled during the polling cycle.
2
For example, if the host requests a trigger count (command <T>) from De-
coder 02, it will transmit the data string 02<T>CR
3
to the concentrator. The
concentrator takes this command, strips off the 02 and substitutes the hex
value 1F as shown in the following select sequence (figure 2-3).
Figure 2-3 Select Sequence
Note:
Commands from the host must be sent as a data block or as a string
from a softkey because hand entry is too slow to prevent the concentrator from
timing out between characters.
A RES (reset) is the first command in the select sequence. The 1F hex is the
select address associated with the decoder’s 02 address (see Table A-4, “Mul-
tidrop Address Characters,” on page A-5). It is followed by a REQ (request).
The decoder responds with its own select address, 1F hex, and an ACK (ac-
1. A retry can be triggered by a NAK or a timeout. A reset occurs after the retry limit (three) has
been reached, or an ACK is sent by the other device.
2. See your decoder or scanner user's manual for specific configuration and operation com-
mands.
3. The carriage return is the default ETX character.
RES 1F REQ
1F ACK
STX <T> ETX LRC
1F ACK
Concentrator
Decoder 02
RES
Start of Sequence
End of Sequence
Summary of Contents for MS-5000
Page 1: ...MS 5000 Multidrop Concentrator User s Manual P N 83 005000 REV J...
Page 8: ...viii MS 5000 Multidrop Concentrator User s Manual...
Page 52: ...Chapter 3 Menu Configuration 3 18 MS 5000 Multidrop Concentrator User s Manual 3 Serial Config...
Page 66: ...Chapter 4 Serial Commands 4 14 MS 5000 Multidrop Concentrator User s Manual 4 Operations...
Page 90: ...A 14 MS 5000 Multidrop Concentrator User s Manual Appendices...
