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5.0 Instruction Set Overview (Continued)
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 XVII
shows the conditional call instruction syntax and operation.
The return instruction complemetns the above call instructions.
Two versions of the return instruction exist, the uncondtional
return and the conditional return. When the unconditional
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
flags, and the register bank selection. Table XVIII 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 return
instruction has two possible syntaxes. Table XIX 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
XII and Table XIII for the listing of "'" and "cc", respectively.
TABLE XVII. Conditional Call Instruction
Syntax Instruction Operation Operand Range
LCALL Rs, p, s, nn If the bit of register "Rs" in position
"p" is in the state "s" then
PC & [GIE) & ALU flags &
reg. bank selection -+ Address Stack
nn -+ RC
End if
Note: PC = Program Counter; contents inHially points to instruction following call.
[GIEI = Global Interrupt Enable bit
& = concatenation operator, combines operands together forming one long operand.
0,64k
Addressing Mode
Register, Absolute
TABLE XVIII. Unconditional Return Instruction
RET
Syntax
(g (, rfll
Instruction Operation
Case "g" of
0: leave [GIE) unaffected, (default)
1: restore [GIE) from Address Stack
2: set [GIE)
3: clear [GIE)
End case
If "rf" = 1 then
restore ALU flags from Address Stack
restore register bank selection from Address Stack
Else (the default)
leave the ALU flags and register bank selections unchanged
End if
Address Stack -+ PC
Note: PC = Program Counter
[GIEI = Global Enable bit
II = surrounds optional operands; not part of the instruction syntax.
Optional operands may either be specified or omitted.
RETF
Rcc
Syntax
f, s (, (gl, (, rfll
(g (,rfll
TABLE XIX. Conditional Return Instruction
Note: See Table XVIII for an explanation of "RET (g (, rfll"
(I = SUrrounds optional operands; not part of the instruction syntax.
Optional operands may either be specHied or omitted.
Instruction Operand
lithe flag "'" is in the state "s" then perform a RET (g (, rf) )
If the condition "cc" is met then perform a RET (g (,rf) )
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