dp8344b National Semiconductor Corporation, dp8344b Datasheet - Page 150

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

Figure 6-1 if condition is not met
Figure 6-2 if condition is met
6 0 Reference Section
RETF Conditional Return
Rcc
Syntax
RETF f s
Rcc
Affected Flags
If rf
Description
Conditionally returns control to the last instruction address
pushed onto the internal Address Stack by popping that ad-
dress into the Program Counter if the state of the flag refer-
enced by f is equal to the state of the bit s or optionally if
the condition cc is met See the tables on the following page
for the flags that f can reference and the conditions that cc
may specify The conditional 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 (g
restored from the Address Stack (g
cleared (g
sumed The second optional operand rf determines if the
ALU flags and register bank selections are left unchanged
(rf
operand is omitted then rf
Example
This example demonstrates both syntaxes of the condition-
al return instruction testing for a carry result from a previous
instruction (i e
return occurs else the next instruction following the return
is executed The current environment is left unchanged
Instruction Format
T-states
2 if condition is not met
3 if condition is met
Bus Timing
Operation
If flag f is in state s then
End if
15
1
e
RETF 001B 1
RC
Case g of
End case
If rf
End if
Address Stack
e
0) or restored from the Address Stack (rf
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
0
e
1 then N Z C and V
g rf
1 then
1
e
0
3) If the g operand is omitted then g
Opcode
g
1
x
C
rf
1
e
PC
1) If the condition is met then the
1
(optional syntax)
If C
If C
e
1
0 is assumed
e
e
0
1 then return
1 then return
6
v
00 GIE not affected
01 Restore GIE
10 Set GIE
11 Clear GIE
g
(Continued)
e
1) set (g
rf
4
3
s
e
1) If the rf
e
2
e
0 is as-
2) or
f
e
0)
0
150
value for the position of DAV in TSR
Z
NZ
EQ
NEQ
C
NC
V
NV
N
P
RA
NRA
RE
NRE
DA
NDA
TFF
NTFF Transmitter FIFO Not Full
Note The value of f for DAV differs from the numeric
cc
0
1
2
3
4
5
6
7
f
Flag Reference Table for ‘‘f’’
Zero
Not Zero
Equal
Not Equal
Carry
No Carry
Overflow
No Overflow
Negative
Positive
Receiver Active
Not Receiver Active
Receiver Error
No Receiver Error
Data Available
No Data Available
Transmitter FIFO Full
Condition Specification Table for ‘‘cc’’
(binary)
(000)
(001)
(010)
(011)
(100)
(101)
(110)
(111)
Meaning
Flag Referenced
Z
C
V
N
RA
RE
DAV
TFF
in CCR
in CCR
in CCR
in CCR
in TSR
in TSR
in TSR
in TSR
Condition Tested for
Z
Z
Z
Z
C
C
V
V
N
N
RA
RA
RE
RE
DAV
DAV
TFF
TFF
e
e
e
e
e
e
e
e
e
e
e
e
e
e
e
e
e
e
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0