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--- tutorials:assemblers [2023/09/23 22:20]
sm5por [Instructions]
+++ tutorials:assemblers [2024/05/20 15:54] (current)
sm5por [Instructions] User I/Omode
@@ Line 102: / Line 102: @@
 === Input/output instruction set ===
-//**Note:** I/O instructions are not available when the processor is in user mode, but can be executed only by the operating system kernel in system (privileged) mode. They are also specific to the I/O hardware architecture of the each processor's brand and model. They are thus of limited interest to regular application programmers under most operating systems.//
+//**Note:** I/O instructions are not available when the processor is in user mode, but can be executed only by the operating system kernel in system (privileged) mode. They are also specific to the I/O hardware architecture of the each processor's brand and model (DEC KA/KI/KL, DEC KS, SC, XKL). They are thus of limited interest to regular application programmers under most operating systems.//
+//In TOPS-20, there is a USRIO system call allowing aprivilegedprocess totemporarily enter User I/O mode (where the UIO bit ofthe processor status word isset so, that I/O operations can be executed.//
 ==== Interrupt system ====

TOPS-20 User Wiki