Arcam DV79 - Manual (Page 27)

DV79
E-26
E
n
g
li
s
h
DV79
E-27
Appendix: Serial programming interface
Introduction
This section of the document describes the remote control protocol for controlling the DV79 via the
RS232 interface.
Conventions
n The remote controller is referred to as the ‘RC’, with the DV79 called the ‘DV79’.
n All values in this section are hexadecimal values, unless otherwise specified.
Data transfer format
n Transfer rate: 19,200bps.
n 1 start bit, 8 data bits, 1 stop bit, no parity, no flow control.
Command and response formats
Communication between the RC and the DV79 takes the form of sequences of ASCII characters, with
all commands and responses having the same basic format. With the exception of status triggers (see
below), the DV79 shall transmit only to respond to communication from the RC. The DV79 shall always
respond to a received command.
Each transmission by the RC shall be five bytes long in the following format:
<STR> <CC> <P1> <P2> <ETR>
n STR (Start transmission): 0x21
n CC (Command code): the code for the command
n Px (Parameter code): the parameters for the command
n ETR (End transmission): 0xD
Each response by the DV79 shall be seven bytes long in the following format:
<STR> <RC> <AC> <P1> <P2> <P3> <ETR>
n STR (Start transmission): 0x21
n RC (Reply code): = command code
n AC (Answer code): answer code (see below)
n Px (Parameter code): the parameters for the reponse
n ETR (End transmission): 0xD
The RC shall transmit commands and receive answers according to the following procedure:
1. The RC shall transmit a command.
2. Having issued a command, the RC shall wait at least 100ms before transmitting a subsequent
command (otherwise commands may be lost). Ideally, the RC shall wait for an answer from the
DV79 before issuing the next command.
3. The RC shall analyse the RC, AC and Px values of a received message to decide whether the
command has been executed normally.
4. The time from the completion of command transmission by the RC to the beginning of the
response by the DV79 shall be maximum two seconds.
5. The DV79 shall not accept any commands from the RC for five seconds after the power switch is
turned on or a ‘power-on’ command is recieved.
The exception to the above communication protocol is when ‘status triggers’ are enabled by the RC (using
the ‘Status Triggers’ command). In this case, the DV79 shall transmit messages whenever the status of
the player changes. These messages shall be transmitted by the DV79 at asynchronous intervals.
State changes as a result of other inputs
It is possible that the state of the DV79 may be changed as a result of user input via the front panel
buttons or via the IR remote control. Changes resulting from these inputs shall be relayed to the RC
(using the appropriate message type) only if ‘status triggers’ have been enabled by the RC.
For example, if the user changed the front panel display brightness using the
DISP button on the remote
control, a display message (defined below) would be sent to the RC. A similar action would be taken for
all other state changes.
Answer codes
The following answer codes are defined:
n Command OK ‘@’ (0x40): The command has been accepted and processed completely.
n Command ACC ‘A’ (0x41): The command has been accepted but not yet processed fully.
n Status update ‘B’ (0x42): Status change message
n Invalid command ‘0’ (0x30): The command or command format was invalid
n Invalid request ‘5’ (0x35): The command is not valid for the current player state
If the answer code returned is anything other than ‘Command OK’ or ‘Status update’ then all parameter
fields in the return message become ‘reserved’.