POLLRUN

Syntax: POLLRUN ProgramSlot

Function

Specify a program to run upon a polled-input event.

• ProgramSlot is a variable/constant/expression (0 - 7) that specifies the program slot to run when a polled-input event occurs.

Quick Facts

Explanation

The POLLRUN command is one of a family of unique "polling" commands on the BS2p, BS2pe, and BS2px modules. The other commands in this family include POLLIN, POLLMODE, POLLOUT and POLLWAIT. The POLLRUN command is used to specify a program slot to run in response to a polled event. This activity can occur in between any two instructions within the rest of the PBASIC program.

The "polling" commands allow the BASIC Stamp to respond to certain I/O pin events at a faster rate than what is normally possible through manual PBASIC programming. The term "poll" comes from the fact that the BASIC Stamp's interpreter periodically checks the state of the designated polled-input pins. It "polls" these pins after the end of each PBASIC instruction and before it reads the next PBASIC instruction from the user program; giving the appearance that it is polling "in the background". This feature should not be confused with the concept of interrupts, as the BASIC Stamp does not support true interrupts.

The following is a simple example of the POLLRUN command:

Setup:
  POLLIN 0, 0
  POLLRUN 1
  POLLMODE 3

Main:
  DEBUG "Waiting in Program Slot 0...", CR
  GOTO Main

The first line of the above code will set up I/O pin 0 as a polled-input pin looking for a low (0) state. The second line, POLLRUN, tells the BASIC Stamp that when I/O pin 0 goes low, it should switch execution over to the program residing in program slot 1. The third line, POLLMODE, activates the polled-run configuration.

Once the BASIC Stamp reaches the Main routine, it will continuously print "Waiting in Program Slot 0..." on the PC screen. In between reading the DEBUG and GOTO commands, however, the BASIC Stamp will poll I/O pin 0 and check for a high or low state. If the state of pin 0 is high, it will do nothing and continue as normal. If the state of pin 1 is low, it will switch execution over to the program in slot 1 (the second program is not shown in this example). The switch to another program slot works exactly like with the RUN command; the designated program is run and the BASIC Stamp does not "return" to the previous program (similar to a GOTO command).

Note that in order for the polled-run activity to occur, the poll mode must be set to either 3 or 4 (the two modes that activate polled-run). Also note, that the polled-run modes, 3 and 4, are unique. As soon as the polled-run action occurs, the mode switches to 1 (deactivated, saved) or 2 (activated, outputs), respectively. This is so that the BASIC Stamp doesn't continuously go to the start of the designated program slot while the polled-inputs are in the desired poll state. Without this "one shot" feature, your program would appear to lock-up as long as the polled-inputs are in the designated state.

After the program switch takes place, the ProgramSlot value is maintained. Any future change to poll mode 3 or 4, without another POLLRUN command, will result in the previously defined program slot being used.