LAMBDA DG-4 & 5 PLUS/USB OPERATION MANUAL – REV.
47
4.1.3
Command Codes
All commands to the Lambda DG-4 correspond to an 8-bit binary value (not all of the
possible 256 values are utilized). The binary values that are used can be classified in the
following way:
Table 4-8. Command code types.
Value range
(Decimal, hexadecimal,
binary)
Command Type
0 – 15
00 - 0F
00000000 - 00001111
MOVE ON COMMAND to the corresponding FILTER
NUMBER (i.e., immediately after receiving the command).
16 - 31
10 - 1F
00010000 - 00011111
MOVE ON TRIGGER to the corresponding FILTER
NUMBER (move only if triggered by Strobe, Synch, or
Synch gated by Strobe).
32 - 255
20 - FF
00100000 - 11111111
Special commands (22 in all)
The first 16 binary values (00000000-00001111) are read as “filter change” commands that
take effect immediately (i.e., “MOVE ON COMMAND”). Each one selects the FILTER
NUMBER that corresponds to the command’s decimal value (0 to 15). Another way of stating
this is that when the 4 most significant bits of the 8 bit binary value all equal 0 (data input
lines 6-9 are all LOW) the 4 least significant bits (data input lines 2-5) will be treated as a
four place binary number whose decimal value corresponds to the desired FILTER NUMBER
(0-15).
The next 16 binary values (00010000-00011111) are also read as “filter change” commands.
These commands will not be executed, however, until the next “trigger” (STROBE or SYNC
PULSE, depending on the mode that is active) has been detected. Each of these commands
selects the FILTER NUMBER that corresponds to the command’s decimal value minus 16.
If, for example, you want to select FILTER NUMBER 6 on the next STROBE PULSE, you
would send the binary equivalent of the decimal number 22 (00010110). Another way of
describing these commands is as follows. When the binary value of the three most- significant
bits is 0 (data input lines 9, 8, and 7 are all LOW), and the next least-significant bit’s binary
value is 1 (data input line 6 is HIGH), then the four least-significant bits (data input lines 5,
4, 3, and 2) are treated as a 4-bit binary number that corresponds with the desired FILTER
NUMBER (0 - 15).
4.1.4
Busy Line
The Lambda DG-4 parallel interface has only one output line, BUSY. The first response of
the unit to a new command is to set the BUSY output line HIGH. The BUSY line will stay
HIGH until the control unit is ready to accept new data..
The status of the 8 input lines is not checked while the BUSY line is HIGH! There is a short
period (as much as 50 microseconds) between when the control unit detects a new value and
the BUSY line is set HIGH. Thus, checking the status of the BUSY line within about 100
microseconds of changing the input lines may give a misleading result.
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