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SYSCALL     System Call     Rabbit 3000A/4000/5000 Instruction

Opcode	Instruction	Operation
ED 75	SYSCALL	SP = SP-2; PC = {R,0x60}

Clocks	8-Bit Access	16-Bit Unaligned	16-Bit Aligned
Rabbit 4000	10	n/a	n/a
Rabbit 5000	13	13	11

Flags				ALTD			IOI/IOE
S	Z	L/V	C	F	R	SP	S	D
-	-	-	-

Description

Pushes PC on the stack and then resets the PC to the interrupt vector address represented by IIR:0x60, where IIR is the address of the interrupt table and 0x60 is the offset into the table. The address of the vector table can be read and set by the instructions LD A,IIR and LD IIR,A respectively, where A is the upper nibble of the 16-bit vector table address. The vector table is always on a 100h boundary.

SYSCALL is essentially a new RST opcode, added to allow access to system space without using one of the existing RST opcodes. It will put the processor into System mode and execute code in the corresponding interrupt-vector table entry.