Introduction   ZCPR3 Flow Control
End IF         
IFEND
Raise IF       
IFT/IFF
Test IF        
IFTEST
Toggle IF      
IFELSE
:Introduction to ZCPR3 Flow Control

Basic Defintion of Flow Control:

     Alì commanä sequenceó issued undeò ZCPR³ caî bå thoughô �
tï  executå  withiî  á TRUÅ flo÷ controì  state®   Thaô  is¬ �
wheneveò  á commanä ió executeä undeò ZCPR3¬  thå  statå  oæ �
flo÷ controì ió TRUE®  Iæ thå statå oæ flo÷ controì ió FALSÅ �
theî nï commandó excepô flo÷ commandó wilì bå executeä untiì �
the state of flow control becomes TRUE.

Background:

     Wheî ZCPR³ firsô comeó up¬ thå statå oæ flo÷ controì ió �
alwayó  TRUE®   Anù commanä issueä wilì bå executed®   Iæ  á �
Flo÷   Commanä  Packagå  ió  installeä  whicè  supportó  thå �
IF/ELSE/FÉ (Enä IF© commands¬ theî thå statå oæ flo÷ controì �
caî bå changeä bù useò commands®  Foò example¬ thå followinç �
terminal session illustrates:


SCR>; any command will execute now
SCR>era *.bak
No Files
SCR>dir
MYFILE  .TXT  |  OBJECT  .BIN
SCR>; we can set a flow control state to be false
SCR>IF F
 IF F
SCR>; no command will execute now
SCR>dir
SCR>else
 IF T
SCR>dir
MYFILE  .TXT  |  OBJECT  .BIN
SCR>FI
 No IF
SCR>


     Hence¬   wheî  anù  commanä  ió  executed¬  beforå  thå �
executioî  actuallù begins¬  ZCPR³ wilì looë tï seå  iæ  thå �
statå oæ thå flo÷ controì ió TRUE®  Sucè ió thå caså wheî wå �
arå  noô withiî aî IÆ conditioî oò wheî wå arå withiî onå oò �
more IF conditions, all of which are TRUE.

     ZCPR³ allowó thå useò tï bå nesteä intï IFó uð tï eighô �
(8©  leveló deep®   Thaô is¬  thå structurå oæ  hió  commanä �
sequenceó  caî takå thå forí oæ somethinç likå thå followinç �
which can be nested into 8 levels of IFs:


<set of commands>
IF T
     <set of commands>
     IF T
          <set of commands>
          IF T
               <set of commands>
          FI
          <set of commands>
     ELSE
          <set of non-executed commands>
          IF T
               <set of non-executed commands>
          FI
     FI
ELSE
     <set of non-executed commands>
FI


     Commanä  structureó likå thoså presenteä abovå arå  no÷ �
possiblå undeò ZCPR3®   Essentially¬  ZCPR³ commandó caî no÷ �
take the form of a programming language in their own right.     

     Thå seô oæ routineó availablå iî thió parô oæ Z3LIÂ arå �
useä tï providå thå programmeò á simplå interfacå tï controì �
thå flo÷ controì withiî (anä outside© hió program®   Hå can¬ �
undeò hió owî control¬  issuå commandó tï:

     ® enteò thå nexô IÆ leveì iî á TRUÅ oò FALSÅ condition,
     . toggle the state of the current IF level,
     . drop down to the previous IF level,
     . determine the current IF level number,
     . or multiples of the above


:End IF Level


Z3LIB Routine: IFEND


Function:
     Droð  tï  thå  previouó IÆ level®   Iæ thå  prograí  ió �
currentlù withiî onå oò morå IFs¬  IFENÄ wilì droð iô tï thå �
next IF level down, terminating the current IF level.

     Naturally¬  foò á transienô tï bå executinç now¬  therå �
ió  currentlù  eitheò nï IÆ leveì oò therå ió  á  TRUÅ  flo÷ �
controì  statå (alì preceedinç IFó arå TRUE)®   Iæ wå arå aô �
somå  IÆ level¬  callinç IFENÄ dropó uó intï thå  preceedinç �
one.


Inputs: None


Outputs: A=0 and Zero Flag Set (Z) if no IF level
          A=0FFH and NZ if IFEND is successful



Registers Affected: PSW


Side Effects: None


Special Error Conditions: None

:Raise IF


Z3LIB Routine: IFT/IFF


Function:
     Raiså thå flo÷ controì statå intï thå nexô leveì oæ IF®  �
IFÔ  raiseó  thå statå intï thå nexô leveì anä  setó  iô  tï �
TRUE¬  whilå  IFÆ  raiseó thå statå intï thå nexô leveì  anä �
sets it to FALSE.

     Thå flo÷ controì statå caî supporô eighô (8© leveló  oæ �
IFs¬  anä  IFÔ  anä IFÆ returî erroò codeó indicatinç iæ  aî �
overflo÷  (anä subsequenô failurå tï enteò thå  nexô  state© �
occurred.


Inputs: None


Outputs: A=0 and Zero Flag Set (Z) if IF level overflow
          A=0FFH and NZ if IF level OK



Registers Affected: PSW


Side Effects: None


Special Error Conditions: None

:Test IF


Z3LIB Routine: IFTEST


Function:
     Tï  determinå thå currenô IÆ level®   IFTESÔ returnó  á �
valuå froí ° tï ¸ iî thå Á register¬  indicatinç thå currenô �
IÆ level®  Iæ A=0¬ therå ió nï currenô IF®  Thå Zerï Flaç ió �
set accordingly, so the following can be done:

          ext  IFTEST
          ...
          call iftest    ;get IF level
          jz   noif      ;process if not any IF level
          cpi  8         ;test for max IF level
          jz   atmax     ;process if at max IF level
          ...


Inputs: None



Outputs: A = number of current IF level, Zero Flag set
               accordingly


Registers Affected: PSW


Side Effects: None


Special Error Conditions: None

:Toggle IF


Z3LIB Routine: IFELSE


Function:
     Togglå  thå  TRUE/FALSÅ statå oæ thå currenô IÆ  level®  �
IÆ thå prograí ió currentlù withiî aî IÆ leveì (theî iô MUSÔ �
bå withiî á TRUÅ IÆ level)¬ callinç IFELSÅ (aî odä numbeò oæ �
times© toggleó thå IÆ leveì tï FALSE®   Twï calló tï  IFELSÅ �
(anù  eveî numbeò oæ calls© resulô iî thå IÆ leveì remaininç �
aô TRUE.


Inputs: None


Outputs: A=0 and Zero Flag Set (Z) if no current IF
          A=0FFH and NZ if successful



Registers Affected: PSW


Side Effects: None


Special Error Conditions: None