ZBasic System Library
196
ZBasic Microcontrollers
Type
Subroutine
Invocation
OpenDAC(channel, mode)
OpenDAC(channel, mode, stat)
Parameter
Method
Type
Description
channel
ByVal
Byte
The channel to use for DAC generation.
mode
ByVal
integral
The desired DAC mode (see discussion below).
stat
ByRef
Boolean
The variable to receive the status code.
Discussion
This subroutine prepares a DAC channel for generating an analog voltage level. The pins on which an
analog level may be generated depends on the target device. See the Resource Usage sub-section
Digital-to-Analog Converters for details on the available analog output pins.
DAC Mode Constituent Values
Function
Hex Value
Bit Mask
Dual Output
&H8000
1x xx xx xx xx xx xx xx
Single Output
&H0000
0x xx xx xx xx xx xx xx
Automatic Refresh
&H4000
x1 xx xx xx xx xx xx xx
Manual Refresh
&H0000
x0 xx xx xx xx xx xx xx
Internal 1-volt Reference
&H0000
xx xx xx xx xx xx xx 00
AVcc Reference
&H0001
xx xx xx xx xx xx xx 01
PortA Aref Reference
&H0002
xx xx xx xx xx xx xx 10
PortB Aref Reference
&H0003
xx xx xx xx xx xx xx 11
It is important to note that the mode parameter value is only used for the first OpenDAC() call for each
channel pair. That is to say, if one channel of a pair is already open when OpenDAC() is called, the mode
parameter is ignored.
The shaded portion of the table above applies only to non-USB xmega devices. For these devices, to
used dual output mode, the DAC values must be updated at least every 30uS. This will be done
automatically if the Automatic Refresh bit is set in the mode parameter. Otherwise, your application will
need to ensure that the DAC values are updated frequently enough to prevent drooping of the DAC
output.
The analog value output by the DAC will be approximately equal to the 12-bit digital value set for each
channel (see the DAC() subroutine) divided by 4095 and multiplied by the reference voltage. The choice
of four reference voltages available is made by the least significant two bits of the mode parameter value.
For the PortA and PortB Aref Reference, the table below indicates the pin to which the desired reference
voltage should be applied.
DAC Reference Voltage Pins
ZBasic Target
Aref A
Aref B
ZX-24x, ZX-24u
20, A.0
7, B.0
ZX-32a4
40, A.0
4. B.0
ZX-128a1
95, A.0
5, B.0
ZX-24xu
36, A.0
28, B.0
xmegaA1, xmegaA1U
95, A.0
5, B.0
xmegaA3, xmegaA3U, xmegaA3B, xmegaA3BU,
xmegaD3
62, A.0
6. B.0
xmegaA4, xmegaA4U
40, A.0
4. B.0
xmegaD4
40, A.0
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