Digitally Controlled Analog I/O Processor
7
MX839 PRELIMINARY INFORMATION
After enabling conversions the user must allow time for all enabled channels to be digitized before reading the results via
the ‘C-BUS’. The minimum required time to wait is:
T
CONV_MAX
=
(10 + 2)
' Number of Enabled Inputs'
f
A/D_CLK
[Seconds]
Upon disabling conversions the data for the most recent conversion completed for each channel will be available via the
‘C-BUS’ commands ‘READ A/D DATA x’ (addresses $DC, $DD, $DE, $DF) for input channels 1 through 4 respectively.
Do not forget to re-enable conversions by setting A/D control register bit 5, the READ bit, back high after reading the
desired A/D results. Note that the Magnitude Comparators (see section 4.4) can be configured to monitor the A/D channel
data in order to minimize the software burden of continuously reading the A/D channel data. It is not recommended to
issue ‘READ A/D DATA x’ commands without first setting A/D control register bit 5, the READ bit, low.
An Example C-BUS transaction to do a conversion and read of A/D Channel 1:
HEX
ADDRESS/
COMMAND
$01
$D0
$D7
$D7
$DC
$D7
WRITE
DATA
BYTE 1
N/A
$03
$70
$50
N/A
$70
READ
DATA
BYTE 1
N/A
N/A
N/A
N/A
xxxxxxxx
N/A
READ
DATA
BYTE 2
N/A
N/A
N/A
N/A
000000xx
N/A
Reset Device
Set f
A/D_CLK
DIVIDER = 4
Enable conversion on A/D Channel 1
Disable conversions after waiting T
CONV_MAX
Read A/D Channel 1 Data
Re-enable conversion on A/D Channel 1
COMMENT
4.4
Magnitude Comparators and Interrupt Request
High and low digital comparator reference levels are provided for the four digital magnitude comparators via the 'C-BUS'
interface. The digital input to the comparators is provided by the most significant 8 data bits of each A/D channel
When the sampled data falls outside the high or low digital comparator reference levels the status register is updated and
the IRQ pin is pulled low. When a reference level is set to '0', its IRQ is disabled.
4.5
4.5.1
Software Description
Address/Commands
Instructions and Data are transferred via the 'C-BUS' in accordance with the timing information provided in Figure 5.
Instruction and data transactions to and from the FX839 consist of an Address/Command byte followed by either:
(i) a control or DAC data write (1 or 2 bytes) or,
(ii) a status or A/D data read (1 or 2 bytes)
© 1998 MXxCOM Inc.
www.mxcom.com Tele: 800 638-5577 336 744-5050 Fax: 336 744-5054
Doc. # 20480164.002
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