DSZ Tests

Using DSZ Tests

A DSZ test combines two operations into a single instruction. First, it decrements the value in a specified data register. Then, it tests whether the value has reached zero. A DSZ test is particularly useful to limit the number of times a loop repeats.

Available DSZ Tests

When you press [ TESTS ], you can select one of two DSZ tests.
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{ DSZ } - Decrement and skip if zero
[ INV ] { DSZ } - Decrement and execute if zero.

Rules Used in Decrementing

In a DSZ test, "decrement" means that the value in the data register approaches zero, based on the following rules.

If the stored value is greater than 1, the DSZ test subtracts 1 from the value.
If the stored value is less than -1, the DSZ test adds 1 to the value.
If the value is between -1 and 1, the DSZ test stores a zero in the register.

Performing a DSZ Test

To include a DSZ test in a program, use one of the following key sequences:
[ TESTS ] { DSZ } nnn or X
[ TESTS ] [ INV ] { DSZ } nnn or X

Decrement and Skip if Zero

The "decrement and skip if zero" test decrements the value in a specified data register and then tests if the register value equals zero. If the register value does equal zero, the program skips the instruction that immediately follows the DSZ test. If the register value does not equal zero, execution continues in normal sequential order.
dsz

Decrement and Execute if Zero

The "decrement and execute if zero" test decrements the value in a specified data register and then tests if the register value equals zero. If the register value does not equal zero, the program skips the instruction that imediately follows the INV DSZ test. If the register value does equal zero, execution continues in normal sequential order.
invdsz

Example

The DSZ tests offer you a convenient and accurate method of executing a program sequence a predetermined number of times. By using either DSZ or INV DSZ, you can control whether the instruction following the test is executed a specific number of times or skipped a specific number of times.

The following program illustrates the operation of a DSZ test in a loop. The program allows you to enter the initial register value for the DSZ test. It then displays the contents of that data register each time the loop executes.

PC =	Program Mnemonics	Comments
0000	STO C	Stores initial DSZ value
0002	LBL LL	Begins loop
0005	RCL C	Recalls DSZ value
0007	PAU	Displays value
0008	DSZ C	Decrements and tests C
0010	GTL LL	C ≠ 0 - repeat loop
0013	HLT	C = 0 - stop program

Running the Example

Enter 4 into the display and run the program.

Procedure	Press	Display
Display RUN menu	[ RUN ]
Enter count value	4
Run the program	{ PGM }



Program halts when done.

Notice that 0 is not displayed. When the data register is decremented to zero, the program exits the loop and stops the program.

The following shows what appears in the display if you run the program with a negative number and with a number that contains a fractional part.

Enter 4.3 into the display and run the program.