Rockwell-automation 1775-KA PLC-3 Communication Adapter Module User Ma Instrukcja Użytkownika Pobierz pdf (Strona 228)

Detailed Flowcharts

Appendix D

D18

WAKEUP without losing immediate control of the processor. If B wakes

up A, context switching would be deferred until B itself has executed a

SLEEP.

A third alternative would cause a context switch if a process performed a

WAKEUP on a higher priority process. If a WAKEUP had been

performed on a lower priority process, the context switch would be

deferred until the first process has gone to sleep.

The first alternative is the result of implementing the driver totally at the

interrupt level where scheduling is dictated by the interrupt daisy chain

hardware.

The third alternative would be used if the driver were implemented as

tasks under a multitasking operating system. Such an implementation

might be easier, but would probably be limited to lower communication

rates.

At powerup, the Z80 processor starts executing code at location 0. The

POWERUP subroutine starts at XMIT and RCVE processes by executing

a SPAWN. A SPAWN is very similar to a WAKEUP except that the

corresponding SLEEP is imaginary and is located prior to the first

instruction of the spawned process.

Figure D.21

POWERUP

Routine

POWERUP

SPAWN

RCVE

SPAWN

XMIT

Continue

Initialization

10091–I

POWERUP

1 2 ... 223 224 225 226 227 228 229 230 231 232 233 ... 238 239

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