 |
 |
|
 |
 |
ZBasic System Library
170
ZX Microcontroller Family
OpenDAC
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 table below
indicates the available channels and the corresponding DAC hardware used. See the description of
DAC() for additional details on the DAC channels.
Supported DAC Channels
ZX Models
DACB
DACA
ZX-24x
Chan 1, Pin 8
Chan 2, Pin 9
ZX-32a4
Chan 1, Pin 6 (B.2)
Chan 2, Pin 7 (B.3)
ZX-128a1
Chan 1, Pin 7 (B.2)
Chan 2, Pin 8 (B.3)
Chan 3, Pin 97 (A.2)
Chan 4, Pin 98 (A.3)
ZX-24xu
Chan 1, Pin 26 (B.2)
Chan 2, Pin 25 (B.3)
Note, particularly, that the ATxmega can produce two analog outputs from a single DAC. In the table
above, channels 1 and 2 are the two outputs from one DAC and channels 3 and 4 are the two outputs
from the second DAC (if available). In order to use the second channel on a given DAC, the first channel
must have been opened in dual output mode (see the table below). Also note that using both outputs
from a DAC will result in analog levels with significantly more noise due to the sample-and-hold and
automatic refresh circuitry employed. For this reason, it is generally recommended to use single output
per DAC.
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 the OpenDAC() is called, the mode
parameter is ignored.
For 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 if the DAC
output.
|
 |
|