Liren Large Software Subsidy 13/13.iso/p/p078/7.img/TUTOR.PLB/UNTIL.PLD

Text File | 1990-12-11 | 768 b | 27 lines

                            GRAY CODE COUNTER

Here is a Gray code counter tested with the aid of an UNTIL clause.  An
explanation of the UNTIL clause appears in Chapter 11 of the reference
guide.

|PAL16R8 in:RESET, out:Q[3..0], clock:CLOCK
|
| Map:  Q[3..0] -> Q[3..0]
| { Gray(n) -> Gray((n+1)\16), RESET'
|   Gray(n) -> 0,              RESET
|   }
|
| Registers:  CLOCK // Q[3..0]

|Vectors:
|{ Display RESET, CLOCK, Q[3..0], (Q[3..0])s
|
|  Test RESET = 1; CLOCK = 0,1             |Clear the counter
|  Test RESET = 0; CLOCK = 16(0,1)         |Test the full Gray sequence
|
|  Test CLOCK = 16(0,1) UNTIL Q[3..0]==15  |Advance until all bits are set
|  Test RESET = 1; CLOCK = 0,1             |Make sure all bits reset
|  End
|  }