The Pulse Programmer Language

The pulse programmer language is a very simple language providing commands on a higher abstraction level than the Forth language of the card. It would go far beyond the scope of any work except the manual to describe that Forth language. It shall be enough to know that there is a compiler which translates our programs to it. We will focus our attention to some pulse programs we used for our measurements.

  

Figure: An example of a simple echo sequence without phase cycling. The abbreviations denote: GT: amplifier gate; PLS: pulse; GTS: signal gate at the spectrometer; TR: trigger; LT: latch; DW: dwell time; TAU, D1, D2 denote durations according to the Bruker convention. The gates are for the protection of the devices and have to be opened before the signal can pass.

The pulse sequence for a simple echo measurement without phase cycling can be implemented for example in a way like this:

1	PLS [LT] 1U
2	PLS [GT-X] 3U
3	PLS [GTPS] D1
4
5	DLY TAU - 4U
6
7	PLS [LT] 1U
8	PLS [GT+X] 3U
9	PLS [GTPS] D2
10
11	DLY TAU-40U
12
13	PLS [GTS,LT] 3U
14	PLS [GTS,TR] DW+1U
15
16	DLY D0

A sketch of the pulses initiated by this program is drawn in figure . The command DLY switches off all channels. It is important to have it at the end of every pulse program to avoid damages of the power amplifier for example in the case of a system crash. With PLS we tell the card to send a pulse on the corresponding channel for the time specified. The channels [LT], [GT-X], [GT-X], [GTPS] and [TR] are previously defined pulse maks. Their definition is given in the file PULSEDEF.7CF already mentioned. The variables D0, D1, D2, TAU and DW are stored in the command interpreter and can be set from the command line or by a script. Every time they are redefined, the pulse program has to be loaded to the board again.

The echo sequence mentione3d above can also be used to perform T₂ measurements. In order to do that we have to change TAU in a given interval. This can be done automatically with a *.AU script program. Showing an example script for T₂ measurements would involve the explanation of the commands available from the command line interpreter, which is a bit lengthy and does not provide us with much understanding. Some more information can be found in the appendix and in the manual. A sweep in TAU does not in any case involve a recompilation of the pulse program, but the time constant has to be replaced and the program has to be sent to the card again. This procedure is still much faster than transferring the pulse sequence over a serial interface to a device such as the RS-670 word generator.

There are two more commands in the pulse language provided by SeveNMR which are very important to implement more sophisticated pulse sequences. They shall again be shown in an example. We used the following pulse program for T₁ measurements:

1	# D0: repetition delay
2	# D1: duration of the first echo-pulse
3	# D2: duration of the second echo-pulse
4	# D3: pulse distance between the comb pulses
5	# D4: pulse duration of the comb pulses
6	# D5: recovery time
7	# C1: number of comb pulses
8
9	LOOP C1
10	DLY D4
11	PLS [GTPS] D3
12	ENDLOOP
13
14	DLY D5-4U
15
16	PLS [LT] 1U
17	PLS PHL1 3U
18	PLS [GTPS] D1
19
20	DLY TAU-4U
21
22	PLS [LT] 1U
23	PLS PHL2 30U
24	PLS [GTPS] D2
25
26	DLY TAU-40U
27
28	PLS [GTS,LT] 3U
29	PLS [GTS,TR] DW+1U
30
31	DLY D0
32
33	PHL 1 [GT+X]
34	PHL 2 [GT+Y] [GT-Y]

The first seven lines are just comments. The lines 9 to 12 send the comb. The variables C0 to C9 are reserved for integer numbers. Here we use C1 for the number of loops to perform. The time variable D5 denotes the recovery time. After the comb sequence a phase cycling pulse sequence is following. In line 17 we make use of a phase list. A phase list is a list of pulse masks which are subsequently sent to the output every time when the phase list is called. In our example there is therefore no point in using the phase list 1, since it could directly be inserted in line 17. The second pulse is -- due to the phase list 2 -- changing between [GT+Y] and [GT-Y]. There may be at maximum 64 pulses in one phase list. How the pulse masks are defined can be found in the appendix .