Remote-processing RPC-2350 Bedienungsanleitung PDF herunterladen (Seite 57)

INTERRUPTS CHAPTER 13

13-2

jumper s from W7 if using external interrupts. IN T1 is

tied to a 10K ohm pull up resistor.

The O N ITR n GO SUB line/label tasking statem ent is

used to initialize interrupts 0 and 1.

INT 0 and INT 1 are level sensitive. As long as the line

is low, an interrupt is generated. This can be a blessing

and curse, depending upon the application. Make sure

you turn off or reset your external hardware interrupt

source before executing a RETURN ITR n.

Hardware service routines require a RETURN ITR n at

the end of the subroutine. This will re-enable the

particular interrupt. If, for some reason you do not want

the interrupt again, you can just RETURN. Some

applications may actually require a delayed RETURN

ITR. This is true if you are monitoring a slow moving

pulse at the counter. When an interrupt is generated, the

low signal output may not go away by the time the

interrupt is finished. You can simply set a flag to let the

main routine know later to re-enable the interrupt when

the condition is gone. See CNTR2.BAS for an example.

Later you can execute RETUR N ITR n to re-enable it.

The CLOC K1. BAS routine shows how interr upt 0 is

used.

INT1 is available at J10-2. It is active low, level

sensitive, and is used in conjunction with the counter

carry or bor row output or an external signal applied to

J10.

NOTE: Interrupts are fr equently tur ned off while

CAMBASIC runs certain time critical code.

Times when interrupts are turned off include

graphic display writing (when sparkle is on),

brief periods when servicing communication

interrupts, and wr iting to Flash. Normally a

pulse 10 micro-Seconds wide can cause an

interrupt. However, if you are saving to flash

or to the graphics screen, the pulse should be

100 micro-Seconds to ensure capture.

NOTE: Interrupt 0 and 1 are level sensitive. As long

as the line is low, another interrupt will be

called as soon as RETURN ITR is executed.

Make sure you clear the source of the interrupt

before executing RETURN ITR.

SOFTWARE INTERRUPTS

Software interrupts are all other “O N” types. T hese

interrupts look for an interrupt condition in software.

The ON BIT, ON INP, ON KEYPAD$, ON COUNT,

and ON TICK routines either scan or count first then

determine if an interrupt should be declared. All of the

above routines oper ate on a 5 mS interval. That is,

every 5 mS lines are scanned, counters checked, and so

on.

Commands that look at digital I/O lines, such as ON

BIT, requir e a stable input condition for at least 5 ms in

order to be recognized.

All of the subroutines use a simple RETURN to continue

execution from where it was interrupted from.

See the examples in the CAMBASIC manual for more

information on using these tasking statements.

COMMANDS

The follow ing comm ands are used for interrupts in

CAMBASIC.

Command Function

ON BIT Interrupt on line change

ON COM$ Interrupt on serial data

ON COUNT Interrupt when count

reached

ON INP Interrupt on bit mask

ON ITR Hardware interrupt

ON KEYPAD$ Interrupt on key press

ON TICK Periodic interr upts

RETURN ITR Return from hardware

interrupt.

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