dp8344b National Semiconductor Corporation, dp8344b Datasheet - Page 26

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

2 0 CPU Description
The BCP has one conditional call instruction capable of
testing any bit in any currently active CPU register This call
only supports absolute instruction addressing Table 2-17
shows the conditional call instruction syntax and operation
The return instruction complements the above call instruc-
tions Two versions of the return instruction exist the un-
condtional return and the conditional return When the un-
conditional return instruction is executed it pops the last
address on the CPU’s Address Stack into the program
counter and it can optionally affect the GIE bit the ALU
Note PC
LCALL
GIE
e
e
Syntax
concatenation operator combines operands together forming one long operand
e
Program Counter contents initially points to instruction following call
Note PC
Note See Table XVIII for an explanation of ‘‘RET g
Global Interrupt Enable bit
Rs p s nn
RET
RETF
Rcc
Optional operands may either be specified or omitted
Optional operands may either be specified or omitted
GIE
Syntax
e
e
e
e
surrounds optional operands that are not part of the instruction syntax
surrounds optional operands that are not part of the instruction syntax
Program Counter
g
Global Interrupt Enable bit
Syntax
f s
g
rf
rf
If the bit of register ‘‘Rs’’ in position
‘‘p’’ is in the state ‘‘s’’ then
End if
g
(Continued)
PC
reg bank selection
nn
Case ‘‘g’’ of
End case
If ‘‘rf’’
Else (the default)
End if
Address Stack
x
rf
TABLE 2-18 Unconditional Return Instruction
TABLE 2-19 Conditional Return Instruction
GIE
Instruction Operation
TABLE 2-17 Conditional Call Instruction
0 leave GIE unaffected (default)
1 restore GIE from Address Stack
2 set GIE
3 clear GIE
restore ALU flags from Address Stack
restore register bank selection from Address Stack
leave the ALU flags and register bank selections unchanged
PC
e
1 then
ALU flags
If the flag ‘‘f’’ is in the state ‘‘s’’ then perform a RET g
If the condition ‘‘cc’’ is met then perform a RET g rf
x
x
rf
PC
Address Stack
’’
26
Instruction Operation
flags and the register bank selection Table 2-18 shows the
syntax and operation of the unconditional return instruction
The conditional return instruction functions the same as the
unconditional return instruction if a desired condition is met
As with the conditional jump instruction the conditional re-
turn instruction has two possible syntaxes Table 2-19 lists
the syntax for the conditional return The ‘‘f’’ flags and the
‘‘cc’’ conditions for the return instruction are the same as
for the conditional jump instruction therefore refer to Table
2-12 and Table 2-13 for the listing of ‘‘f’’ and ‘‘cc’’ respec-
tively
Instruction Operand
Operand Range
0 64k
Addressing Mode
Register Absolute
rf