Motorola 24-Bit Digital Signal Processor, DSP56000 Interrupt Masks Bits 8, Scaling Mode Bits 10

PROGRAMMING MODEL

If	S1=0 and S0=0 (no scaling)
then	S = (A46 XOR A45) OR (B46 XOR B45)
If	S1=0 and S0=1 (scale down)
then	S = (A47 XOR A46) OR (B47 XOR B46)
If	S1=1 and S0=0 (scale up)
then	S = (A45 XOR A44) OR (B45 XOR B44)
If	S1=1 and S0=1 (reserved)
then	the S flag is undefined.

where Ai and Bi means bit i in accumulator A or B.

5.4.2.9Interrupt Masks (Bits 8 and 9)

The interrupt mask bits, I1 and I0, reflect the current IPL of the processor and indicate the IPL needed for an interrupt source to interrupt the processor. The current IPL of the processor can be changed under software control. The interrupt mask bits are set during hardware reset but not during software reset.

I1	I0	Exceptions Permitted	Exceptions Masked
0	0	IPL 0,1,2,3	None
0	1	IPL 1,2,3	IPL 0
1	0	IPL 2,3	IPL 0,1
1	1	IPL 3	IPL 0,1,2

5.4.2.10Scaling Mode (Bits 10 and 11)

The scaling mode bits, S1 and S0, specify the scaling to be performed in the data ALU shifter/limiter, and also specify the rounding position in the data ALU multiply-accumula-

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