Serial Communication
The QSD 204 can be remotely controlled via a host computer or other device (such as a control system) attached to the rear panel Remote connector. The control device (host) can use either Extron’s Simple Instruction Set (SIS) commands or the graphical control program for Windows.
The decoder uses a protocol of 9600 baud, 1 stop bit, no parity, and no flow control.
The rear panel
Pin | Description | 5 | 1 | |
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1 | Input #1 | Contact closure |
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2 | Tx | Transmit data |
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3 | Rx | Receive data | 9 | 6 |
4 | Input #2 | Contact closure | DB9 Pin Locations | |
5 | Gnd | Signal ground | Female | |
6 | Input #3 | Contact closure |
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7 | Input #4 | Contact closure |
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8 | – | No connection |
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9 | – | No connection |
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RS-232 Programmer’s Guide
Host-to-decoder communications
SIS commands consist of one or more characters per field. No special characters are required to begin or end a command sequence. When the QSD 204 determines that a command is valid, it executes the command and sends a response to the host device. All responses from the decoder to the host end with a carriage return and a line feed (CR/LF = 
), which signals the end of the response character string. A string is one or more characters.
Decoder-initiated messages
When a local event such as a front panel selection or adjustment takes place, the QSD 204 decoder responds by sending a message to the host. No response is required from the host. The
(C) Copyright 2002, Extron Electronics, QSD 204, Vx.xx 
The QSD 204 sends the copyright message when it first powers on. Vx.xx is the firmware version number.
C hn X1
(where X1 is the input number)
The QSD 204 sends this response when an input is switched. C = both audio and video were switched.
Error responses
When the decoder receives a valid SIS command, it executes the command and sends a response to the host device. If the QSD 204 is unable to execute the command because the command is invalid or it contains invalid parameters, it returns an error response to the host.
The error response codes and their descriptions are as follows:
E01 – Invalid input channel number (the number is too large)
E10 – Invalid command
E11 – Invalid preset number
E13 – Invalid value (the number is out of range/too large)
E17 – Illegal command for this signal type.