dp8344b National Semiconductor Corporation, dp8344b Datasheet - Page 143

• Manufacturer Part Number: dp8344b
• Description: Biphase Communications Processor?bcp
• Manufacturer: National Semiconductor Corporation

Figure 6-4
6 0 Reference Section
JRMK Relative Jump with Rotate and
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 (e g LJMP) The range
of JRMK is from
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 m
masked m
m
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
Instruction Format
T-states
4
Bus Timing
Operation
Copy Rs to a temporary register
Rotate the register b bits to the right
Mask the most significant m bits and the LSB
Modify the Program Counter
1
15
e
EXX
JRMK
LJMP
LJMP
LJMP
LJMP
Rs
register AND 0
PC
2 causes bits 7 – 6 and the LSB to be masked etc
0
Opcode
x
a
0
e
register(sign extended)
register
Mask on Register
0 causes only the LSB of the displacement to be
e
0
1 causes the MSB and the LSB to be masked
0 1
RTR 1 4
ADDR 0
ADDR 1
ADDR 2
ADDR 7
V W
0
m
a
10
126 to
0 1
m
register
select main A alt B
decode device address
jump to device handler
jump to device handler
jump to device handler
jump to device handler
b
1 0
128 relative to the Program
7
x
x
b
PC
register
(Continued)
4
Rs
TL F 9336 – 8
0
1
2
7
0
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