DP8344 datasheet(143/184 Pages) NSC

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60 Reference Section (Continued)

JRMK

Relative Jump with Rotate and

Mask on Register

Syntax

JRMK

Rs b m

Affected Flags

None

Description

Transfers control to the instruction at the memory address

calculated by adding the contents of the Program Counter

to a specially formed displacement The displacement is

formed by rotating a copy of the source register Rs the val-

ue of b bits to the right masking (setting to zero) the most

significant m bits masking the least significant bit and then

sign extending the result to 16 bits Typically the JRMK

instruction transfers control into a jump table The LSB of

the displacement is always set to zero so that the jump table

may contain two word instructions (eg LJMP) The range

of JRMK is from a126 to b128 relative to the Program

Counter Note that the Program Counter initially contains

the memory address of the next instruction following JRMK

The source register Rs may specify any active CPU register

The rotate value b may be from 0 to 7 where 0 causes no

bit rotation to occur The mask value m may be from 0 to 7

where me0 causes only the LSB of the displacement to be

masked me1 causes the MSB and the LSB to be masked

me2 causes bits 7 – 6 and the LSB to be masked etc

Example

This example demonstrates the decoding of the address

frame of the 3299 Terminal Multiplexer protocol In the ad-

dress frame only the bits 4 – 2 contain the address of the

Logical Unit

EXX

select main A alt B

JRMK

RTR14

decode device address

LJMP

ADDR0

jump to device handler

LJMP

ADDR1

jump to device handler

LJMP

ADDR2

jump to device handler

LJMP

ADDR7

jump to device handler

Instruction Format

10000

Opcode

T-states

Bus Timing

Figure 6-4

Operation

Copy Rs to a temporary register

xregister

Rotate the register b bits to the right

TLF9336 – 8

Mask the most significant m bits and the LSB

V W

xregister

Modify the Program Counter

PC a register(sign extended)

xPC

143

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