English
DT91
E-11
Appendix: Serial programming interface
Introduction
This section of the document describes the remote control protocol for controlling the DT91 via the
RS232 interface.
Conventions
n The remote controller is referred to as the ‘RC’.
n All values in this section are hexadecimal values, unless otherwise specied.
Data transfer format
n Transfer rate: 19,200bps.
n 1 start bit, 8 data bits, 1 stop bit, no parity, no ow control.
Command and response formats
Communication between the RC and the DT91 takes the form of sequences of bytes, with all commands
and responses having the same basic format. Communication between the two is full duplex. The DT91
shall always respond to a received command.
Each transmission by the RC shall be at least ve bytes long in the following format:
<STR> <C
C> <DL> <Da
ta> <ETR>
n STR (Start transmission): 0x21
n CC (Command code): the code for the command
n DL (Data length): the number of data items following this item, excluding the ETR
n Data: the parameters for the command
n ETR (End transmission): 0xD
Each response by the DT91 shall be at least six bytes long in the following format:
<STR> <R
C> <AC> <D
L> <Data> <E
TR>
n STR (Start transmission): 0x21
n RC (Reply code): = command code
n AC (Answer code): answer code (see below)
n DL (Data length): the number of data items following this item, excluding the ETR
n Data: the information associated with this response
n ETR (End transmission): 0xD
Note that the DT91 shall transmit messages whenever its status changes.
State changes as a result of other inputs
It is possible that the state of the DT91 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) as they occur.
For example, if the user changed the front panel display brightness using the DISP button on the remote
control, a display message (dened 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 dened:
n Command OK 0x1: The command has been accepted and processed completely.
n Command Failed 0x0: The command has failed for some reason.
