Remote-processing CAMBASIC Instrukcja Użytkownika Pobierz pdf (Strona 196)

Event Multitasking - 7

Line 110 prints the count in the counter.

Line 120 returns execution to the place where the one– second interrupt occurred.

You can try this by holding down the < ENTER> on your terminal so that it auto– repeats and enters count faster.

INP TASKING

INP tasking lets you react to a combination of on/off conditions at a digital I/O port. T hat is, you may want to detect

when inputs 0, 1 and 7 are high, and inputs 2 and 3 are low, while ignoring the other input lines (4, 5, 6).

There are a total of 8 tasks that can be configured. The ON INP statement sets the interrupt conditions. The START INP

is used to activate the task. STOP INP will deactivate the task. Another STA RT INP will reactivate the task. You do not

need to execute ON INP to start the task again.

Declaring a Task

This is done with the ON INP statem ent. T he syntax is :

ON INP n, address, m ask, com pare GOSUB line/label

Where:

n is the task number. The r ange of n is 0 to 7.

address is the I/O address of the port in interest. The port can be an actual input port like that on an

82C55, a readable latch or an internal CPU register.

mask determines which of the input bits or lines are of interest. For example, if we want to look at

lines 0, 1, 2, 3 and 7, then the mask would be:

10001111

in binary or 8F in hex or 143 in decimal. The “1” bits of the mask are the bits of interest. During

execution the mask is ANDed with the port value.

If the result is equal to the compare parameter, then a interrupt occurs. The program then branches

to the GOSU B line/label.

The inputs are checked 200 (100 in 9 MHz systems) times per second. In most applications, the inputs will be changing

much more slowly. Thus, if a match occur red and remained the sam e for one second, then 200 (100 in 9 MH z systems)

interrupts would occur.

To prevent this from happening, the ON INP operates in the “edge triggered” mode. The program branch occurs only on

the first instance of the match. All subsequent matches are ignored until at least one input changes, so that a match is not

present.

The example below will let you demonstrate the INP task, using a par allel port, a UTB terminal board and clip leads.

10 ON INP 0, 2, 7, 5 GOSUB 60

20 START INP 0

30 PRINT BIN$ (INP (2) )

1 2 ... 191 192 193 194 195 196 197 198 199 200 201 ... 207 208

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Remote-processing CAMBASIC Instrukcja Użytkownika Strona 196