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60 Reference Section (Continued)

RET

Unconditional Return

Syntax

RET

Affected Flags

If rfe1 then N Z C and V

Description

Unconditionally returns control to the last instruction ad-

dress pushed onto the internal Address Stack by popping

that address into the Program Counter The unconditional

return instruction also has two optional operands g and rf

The value of g determines if the Global Interrupt Enable bit

GIE is left unchanged (ge0) restored from the Address

Stack (ge1) set (ge2) or cleared (ge3) If the g operand

is omitted then ge0 is assumed The second optional oper-

and rf determines if the ALU flags and register bank selec-

tions are left unchanged (rfe0) or restored from the Ad-

dress Stack (rfe1) If the rf operand is omitted then rfe0is

assumed

Example

Return from an interrupt

RET

Restore environment

return

Instruction Format

101011111

0000

Opcode

00GIE not affected

01Restore GIE

10Set GIE

11Clear GIE

T-states

Bus Timing

Figure 6-1

Operation

Case g of

0 leave GIE unaffected (default)

1 restore GIE from Address Stack

2 set GIE

3 clear GIE

End case

If rfe1 then

restore ALU flags from Address Stack

restore register bank selection from Address Stack

End if

Address Stack

xPC

ROT

Rotate

Syntax

ROT

Rsd b

Affected Flags

N Z C

Description

Rotates the contents of the register Rsd b bits to the right

and places the result back into that register The bits that

are shifted out of the LSB are shifted back into the MSB

(and copied into the Carry flag) The value b may specify

from 0 to 7 bit rotates

Example

Add 3 to the Address Stack Pointer contained in the Internal

Stack Pointer register ISP

R30

MOVE

ISP R8

get ISP

ROT

R8 4

shift ASP to low order nibble

ADD

3 R8

add 3 to ASP

ROT

R8 4

shift ASP to high order nibble

MOVE

R8 ISP

store new ISP

Instruction Format

11001010

Opcode

Rsd

T-states

Bus Timing

Figure 6-1

Operation

TLF9336 – 12

151

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