ZBasic Language Reference
9
ZBasic Microcontrollers
Option <pin> <pin-state>
This option directive provides a way to configure an I/O pin to be an input or an output. If it is being
configured to be an input, you can further specify whether or not the pull-up resistor is enabled. If it is
being configured to be an output, you can further specify the logic level that you want to be output. This
option directive may only appear in the first module compiled - usually the one containing the Main()
subroutine.
The <pin> element specifies the pin to be configured. The first way to specify the pin to configure is to
use the word Pin followed immediately by a physical pin number, e.g. Pin20. Of course, the set of pin
numbers that can be specified in this way depends on the ZX processor that you are using. For example,
for the 24-pin ZX devices the allowable values are Pin5 through Pin20 as well as Pin25, Pin26 and
Pin27. The second way to specify the pin to be configured is to give the port letter and a bit number of
the port with a period separating them, e.g. C.0. The advantage of the second method is that it is largely
independent of the ZX processor that you’re using.
The <pin-state> element may be one of the entries in the table below:
Pin Configuration Values
Pin State
Meaning
zxInputTriState
The pin should be a tri-state input (pull-up disabled).
zxInputPullUp
The pin should be an input with the pull-up enabled.
zxOutputLow
The pin should be an output set to logic zero.
zxOutputHigh
The pin should be an output set to logic one.
Alternatively, for compatibility with the Option Port directive, the <pin-state> element may be a
quoted string containing a single character T, P, 0 or ¹ corresponding to the entries in the table above.
For convenience when using the 24-pin ZX devices, RedLED and GreenLED are allowed as synonyms
for Pin25 and Pin26 respectively. When using these synonyms the <pin-state> must be specified
as On or Off.
By default, all pins are configured to be inputs with the pullup disabled.
Examples
Option Pin5 zxOutputLow
' make pin 5 an output at logic zero
Option Pin20 "T"
' make pin 20 a tri-state input
Option C.0 zxOutputHigh
' make bit 0 of Port C an output at logic one
Option RedLED On
' turn on the red LED
Option <port> <config-string>
This option directive provides a way to configure an entire I/O port at once instead of doing so pin by pin.
For each bit of the port being configured to be an input, you can further specify whether or not the pull-up
resistor is enabled. For each bit of the port being configured to be an output, you can further specify the
logic level that you want to be output. This option directive may only appear in the first module compiled -
usually the one containing the Main() subroutine.
The allowable values for the <port> element are PortA, PortB, PortC, etc. Note, however, that
PortB and PortD will rarely be used with the 24 pin ZX devices since the many of the pins of those ports
are not directly available. The <config-string> element must be a series of characters, enclosed in
quote marks, which specify for each bit one of four configuration states. The allowable configuration
characters are described in the table below. The <config-string> must contain exactly 8
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