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ZBasic Language Reference
10
ZX Microcontroller Family
Port Configuration Designators
Configuration
Character
Meaning
T
The corresponding bit should be a tri-state input (pull-up disabled).
P
The corresponding bit should be an input with the pull-up enabled.
0
The corresponding bit should be an output set to logic zero.
1
The corresponding bit should be an output set to logic one.
Note that it is not necessary to configure your ports using this option directive. The configuration may
also be done using the System Library subroutine PutPin() or built-in registers like Register.DDRA.
Also, note that if you specify configuration directives for both the pins and the port containing them, the
last occurring directive will prevail.
Example
Option PortA "TPTP0001"
Option Base
Option Base <value>
Default: 0
Although zero-based arrays are common in many programming languages, some people find it easier to
think about arrays being indexed beginning with 1. The Option Base directive is provided to allow you
to specify that the default array base is either 0 or 1, the <value> element of the directive must be one of
those values.
Note that it is not necessary to use this directive to define 1-based arrays. The syntax for array definitions
(see page 17) allows you to specify any base value that you wish for each array, including a negative
base value if you wish. Some programmers believe that it is better to explicitly indicate the base of the
array indices in each definition. That way, you never have to remember or go find out what the default
base might be.
This option does not affect Program Memory data items, they are always 1-based. Moreover, this option
has local scope, i.e., it only affects arrays defined in the same module in which the option appears.
Example
Option Base 1
Option Explicit
Option Explicit
Default: Off
Traditionally, the purpose of the Option Explicit directive has been to require that each variable in
the program be explicitly defined. Historically, early Basic dialects allowed programs to be written so that
when the compiler encountered a new variable name, it automatically created a definition for it. Although
this may have been thought to be a nice feature, it turned out to be the source of many programming
errors and bugs. If you accidentally misspelled a variable name, a new variable was created entirely
unbeknownst to you. Because of this serious drawback implicit variable definition is not supported by
ZBasic. The Option Explicit directive is accepted by the compiler for compatibility reasons but
neither its presence nor its absence affects any aspect of the compiler’s operation.
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