Australian Monitor DMA1 - Manual (Page 31)

S E R I A L R S 4 8 5 C O M U N I C AT I O N
PA G E 3 1 A M I S - D M A 1 I N S TA L L AT I O N & O P E R AT I O N M A N U A L
Reply wait time (CMDR)
This is the delay time before the transmission of a reply message, required
by some control systems to switch between the state of transmission and
the state of reception.
The reply waiting time determines the minimum delay before the DMA1
sends data in reply to the message received from the control system. Set
this time at a value different from 0 only if the control system requires it,
since the delay determines an extension of the time needed to complete the
command.
9.3 “ Framing” error
A framing error may take place if nothing is being transmitted on the
serial line.
In order to avoid this mishap, it is recommended that the control system
ignores all data until it has received one of the STX, ACK or NAK characters
coming from a DMA1.
9.4 NAK reply by a DMA1
The reply with the NAK character is sent from DMA1 to the control system
when any kind of error is detected in the received message.
9.5 Transmitting a command from a control system
When sending a command from the control system to a DMA1, make sure
it is sent after a minimum delay of 10ms after receiving the last instruction
from the DMA1 to ensure the DMA1 has had suffi cient time to process the
last request.
IMPORTANT!
When using an RS485 bus remember to ignore the echo of the
command that is sent from the control system (with RS485 an echo
is always present).
9.6 Basic format of dedicated protocols
The DMA1 supports up to four dedicated RS485 protocols.
Which of these four protocols is used by the serial connection is defi ned in
the confi guration fi le confi g.txt (par. 9.2).
The difference between these four formats is due to the presence or absence
of CheckSum and/or of the end-0f-packet characters CR (Carriage Return,
character 0DH) and LF (Line Feed, character 0AH).
9.7 Basic set-up of data packets
Control code
DMA1 address
Command code
Command data
CheckSum
CR/LF control codes