Mark Levinson 512 - Manual (Page 8)

N o 512 CD/SACD Player Serial Communications Protocol Mark Levinson
5.2 Incoming Messages
The Header Field (1st field) of every external protocol string indicates the type of message contained
within the transmitted string. All incoming messages to the N
o 512 contain the string “RQST” in the header
field. Any other string in the header field indicates an outgoing message. The control source that issued
the Request (RQST) expects a reply within 500ms after receipt of the string to indicate that the message
was received. This response can be an acknowledgement (ACK), the requested action if a data
parameter was requested, or a WAIT to indicate the system has received the command but needs
additional time to process the request.
NOTE: When an incoming request is received, the system acknowledges receipt of the string within
500ms of receiving the incoming message.
5.3 Outgoing Messages
Outgoing Messages are generated to acknowledge an incoming request, to provide requested
information, or to inform of a system action occurring. As with an incoming message, the Header field is
used to indicate the type of message contained within the string. Outgoing messages will be a response
(RSP) to a request or a system generated notification (NTF) message.
5.3.1 RSP – Response to Command Request
An outgoing RSP will be generated as the result of an incoming RQST. In most cases the response is an
acknowledgement (ACK) unless the request is a query “?”. In the case of a query, the RSP contains the
requested parameter, rather than an ACK.
5.3.2 NTF – Notification of System Action
An NTF is generated as the result of a system action occurring. When commands are issued to the
system, they are placed in a queue in the order they are received. When the command is acted upon and
the requested action has completed or occurred, a notification is generated within the system.
Notifications can occur if a user issues a RQST via External Protocol to instruct the system to perform an
action.
When a NTF event occurs, the source field indicates the source of the event:
UI (user interaction)
AV (component generated) fault
It’s important to note that Notifications are only sent to the Controller if they are enabled. See the
Notification Factory Defaults section of this document for the factory default settings. See the External
Protocol Commands section in this document for more information.
5.4 Example Request - RQST
RQST:CS:PWR:ON\r - incoming Request (RQST) from a Control Source (CS) commanding
Power (PWR) ON.
RQST:CS:PWR:?\r - incoming Request (RQST) from a Control Source (CS) querying the Power
(PWR) state.
RQST:CS:PWR:NTF?\r - incoming Request (RQST) from a Control Source (CS) querying the
Power (PWR) Notification state.
RQST:CS:VOL:25.6\r - incoming Request (RQST) from a Control Source (CS) commanding
Volume (VOL) to 25.6.
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