BNC 630 - Manual (Page 47)

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Downloading Modulation Message Data
To download the modulation data, you must send an ASCII message to the 630 through the serial port. To do this, first cable the
PC’s serial port to the 630 as shown in the Remote Operation section of this manual.
The following example has you generate an ASCII disk file and download it to the 630. If the file already has the “W M” header,
you may use the WAVELOAD.EXE utility with the “no header” option (/N) to send the file to the 630. (See the chapter on
Downloading Arbitrary Waveforms for more information on WAVELOAD.EXE). You may also write your own program to send
the data to the 630. If you wish to use your own program, be sure to set the serial port parameters to1 start bit, 8 data bits, 1 stop bit,
and no parity. The baud rate of your program must also match that of the 630. To inspect or change the 630’s baud rate, press the
Mode key and then the Offset key.
Modulation Data is sent to the 630 in Hexadecimal format. (For more information on hexadecimal numbers, refer to the chapter
on Hexadecimal Format in this manual). The message consists of a two character header, a bit count word, and the modulation data
words. It does not matter what mode the 630 is in when the data is downloaded, however you must switch to Internal FSK mode in
order to transmit the message.
Example Message:
The message is best explained by example. An example message is
W M 0012 FE96 AA20 X
which breaks down as follows:
W - This is the first character which tells the 630 to download data from the user
M - This character tells the 630 that the data is MODULATION data (as opposed to an arbitrary
waveform)
0012 - This is the bit count. In this case, the message is 18 bits long (0012 in Hexadecimal is 18 in base 10). 960 bits maximum.
FE96 - This is the first 16 bits (one word) of the binary message. The first bit to be transmitted is the MSB of this word.
AA20 - This is the second 16 bits of the binary message. Since the message is only 18 bits long, only the MSB and the next lower
bit will be sent (in this case a 1 then a 0). After the last bit is sent, the 630 turns off the carrier and awaits another
trigger condition.
X - This character denotes the end of the data and is optional. If the “X” character is missing, the 630 will assume all data
has been sent after 1 second time-out.
The 18 bit message for the data FE96 AA20 is sent as follows:
1111 1110 1001 0110 10
First bit transmitted Last bit transmitted
Since this message is only 18 bits long, the last 14 bits of AA20 are ignored.
Note: For more information on the Hexadecimal format, please refer to the User’s Manual chapter on Hexadecimal Format.
Triggering the Transmission
The Data Modulation mode starts by setting the output frequency to 0 Hz and awaiting a trigger condition.
When a trigger condition occurs, the unit will turn on the carrier and modulate the carrier until all bits have been sent out. After the
message has been transmitted, the 630 will turn off the carrier and await another trigger event.
The 630 will simultaneously accept a trigger from these three sources:
1. Pressing the Trigger key
2. Applying a low-to-high transition on the Ext Trig In connector
3. Sending an ASCII "T" to the RS232 port
Saving the Message
You may save the downloaded message by saving the instrument setup using the STORE/RECALL button. Up to 10 instrument
setups (including 10 messages) may be stored. Modulation data messages are only saved when the unit setup is stored in Internal
FSK mode.