Tektronix Keithley AOM5 Analog Output Module User manual

AOM5

Analog Output Module

Introduction

The AOM5 is a high-speed analog output module provid­ing four independent channels of D/A conversion. A
system strobe feature, supported by two levels of data
latching in the D/A converter, allows all D/A channels to
be updated simultaneously.

TheAOM5 D/A converters offer 13-bit resolution (12 data
bits plus a sign bit). Four output ranges can be independ­ently selected through software for each channel: lOV, SV,
2V, and 1V. The sign bit switches the converter output
either positive or negative, so the effective full-scale reso­lution for a bipolar range is 8192 steps. Programming +OV
or -0V results in the same output. Maximum nonlinearity
is fl.O24%.

The AOM5 analog output circuitry has a 5~s settling time,
and can theoretically achieve output update speeds of
2OOkHz. However, the speed of the computer limits the
rate at which successive output values can be written to the
module, with a typical speed being about 6OkHz for a

1OMHz 80286-based computer.

High-speed operation is supported in Keithley’s KDAC500
software by the ANOUTQ (ANalog OUTput Quick) com­mand. The AOM5 analog output circuitry also offers an

“auto-sequence” mode which can be implemented through
PEEK and POKE commands or assembler language. This
feature makes it possible to write optimized high-speed
analog output routines. It is described later in this manual.

HardwareCompatibility

The AOM5 can be operated in slots 2 through 10 of the
5OOA, 5OOl?, or 556 mainframe. Up to nine AOM5 modules
can be used in these systems for a maximum of 36 analog
output channels. The AOM5 can also be used in the option
slot of the Model 570 or 575 for up to 6 analog output
channels.

The AOM5 uses the voltage reference which is a part of the
system A/D converter circuitry. In the 500~series systems
and Mode1575, the reference is located on the AMM analog
master measurement module plugged into slot 1 of the
system. Where analog input measurements are not needed,

an AOM5 can also be plugged into slot 1 of these systems.
This requires that the optional on-board voltage reference
be populated on the AOM5. This reference circuitry is ex­plained later in this manual under the topic “Using the On­board Voltage Reference”.

Software Compatibility

Keithley’s KDAC500 software fully supports the AOM5. If
you are using third-party software, be certain that the
software is compatible with the AOM5.

The AOM5 can also be programmed by accessing its
command registers. This can be done through any high- or
low-level language by writing directly to the AOM5
Command A (CMDA), Command B (CMDB), and Global
Strobe registers which are explained later in this manual.

Document Number: 501-920-01 Rev. A
Copyright Q1990 Keithley Instruments, Inc., Cleveland, OH 44139 [phone]

AOM5-1

AOM5A

Analog Output Module

3

QQQ 0

B

?gure I. AOM5 Module

Specifications

Channel capacity: 4
Resolution: 13 bits (12 data bits plus polarity bit).

Full-scale Output Ranges: &lOV, &!W, &2V, flV
Output updating: Instantaneous update or global strobe.
Maximum output load: 2wZ minimum. 1OOpF maximum.
Settling time: 5~s to 0.01% flLSB for any step size.
Maximum output update frequency: 2OOkHz
Non-linearity: fl LSB

0

I

CAUTION
Turn off power to the data acquisition system
before you insert or remove any module. To
minimize the possibility of EMI radiation,
always operate the data acquisition system
with the cover in place and properly secured.

CAUTION
Make sure you have discharged any static
charges on your body before handling the

module. You can do this most easily by simply
touching the chassis of a computer or data
acquisition mainframe which is plugged into
agrounded,b-wireoutlet.Avoid touchingcom­ponents or the card edge connector of the
module.

Accuracy:~lOVrange-M.15%‘omV.Otherranges,M.2%
f4mV.

Temperature coefficient: ti.O025% per degree C.

Installation

All features and operating modes of the AOM5 module are
programmable; there areno hardware switches to be set.

AOM5-2

For a compatible multi-slot data acquisition system (e.g.
Model 5OOA, 5OOP, or 556), remove the top cover of the
system by loosening the cover retaining screws located in
the upper corners of the rear panel. Slide the cover back
about one inch and then lift it off. Insert the module in the
desired slot with the component side facing the system
power supply. Replace the system cover.

For a Model 570, install the module in the option slot with
the component side of the board facing upward. Close and
secure the cover.

AOM5

Analog Output Module

For a Model 575, first attach the supplied right-angle
bracket to the module (see Figure 2). Plug the AOM5 into
the option slot with the components facing upward, and
secure the bracket to the rear panel of the system. Close and
secure the cover.

End View

I

Threaded Hole

1

3gure 2. Model 575 Mounting Bracket

Top View

\

,

Connections

The four channels on the AOM5 are accessed through the
quick connect terminals of J2. Each of the four outputs has
two terminal screws: one screw for analog output and one
for analog ground. The channel connections are listed in
Table 1.

the block and insert the bare end of the wire into the corre­sponding hole. Tighten the screw securely to compress the
tab against the wire.

After you have attached all the desired signal wires to a
terminal block, replace the terminalblock by lining it up
with the mating pins on the module and pressing it back
into place.

NOTE
For analog output connections, use shielded
cable to

minimize the possibility of EMI radia­tion. Connect the shield to module analog
ground. Leave the other end of the shield dis­connected.

Output Limitations

The output circuitry of the AOM5 is designed for fast
output settling time.
restrictions as to the output capabilities of each channel.
Generally, there is an upper limit on the amount of capaci­tance and a lower limit to the resistance that can be con­nected across the output. To avoid possible oscillation,
output capacitance must be less than 100pF.

Because of the design, there are

Table 1. J2 Connections

Channel
Number

A quick-disconnect terminal block can be removed from
the module to facilitate making connections. Pull the block
straight off the board with a firm, even pressure. Do not pry
the terminals with a screwdriver or sharp object, or you
may damage the circuit board.

Each individual terminal on a terminal block consists of
a small metal block with a hole and metal compression tab

within the hole. To make connections to a terminal block,
first strip 3/16 of insulation from the end of the wire which

you want to attach. Loosen the desired terminal screw on

If it is necessary to drive a capacitive load larger than
lOOpF, a 1OOzL or larger resistor must be placed in series
with the output. This will slow down the settling time
somewhat, depending on the value of the capacitive load.
A wire jumper is installed on the AOM5 circuit board in
series with each output.

The jumper may be removed and
replaced by a series resistor if desired. The jumpers are
labelled Wl through W4 on the component layout, and
correspond to output channels 0 through 3 respectively.

Similar restrictions apply to the output current, which is
determined largely by the resistive component of the load
connected across the output. If the resistance is too small,
accuracy will suffer. To maintain rated accuracy, the load
resistance should be at least 2w2 at the maximum output of

flOV. Maximum current output is 5mA or less.

If an analog output channel must drive a load with both
low resistance and high capacitance, the output must be
buffered by an external voltage amplifier.

AOM5-3

AOM5A

Analog Output Module

AOM5 Commands and Command Locations

The AOM5 is controlled by writing to the Command A
(CMDA), Command B (CMDB), and Strobe addresses for
the slot in which the module is mounted. Programmable
parameters include selection of channel and range, loading
of data, auto-sequencing control, and strobe. There are no
READ modes for the AOM5. Refer to your data acquisition
system hardware manual for the addresses associated with
the slot where the AOM5 is mounted.

Table 2. Slot-Dependent Memory Locations (hex)

500,570,575 GPIB

I I

SLOT CMDA CMDB
1”

2
3*
4
5
6
7
8**

xxx80 xxx81 0
xxx82 xxx83 2 3
xxx84 xxx85
xxx86 xxx87 6

xxx88 xxx89 8 9
xxx8A xxx8B A
xxx8C xxx8D

xxx8E xxx8F E F
9 XXX90 xxx91
10 xxx92 xxx93

* = Model 575 Physical Slots
** = Model 570 Option Slot

xxx = First three digits of IBIN address, e.g. “ClT

Table 3. AOM5 Command Locations and Functions

Read Functions:

CMDA CMDB

1

4

5
7

B

C

10
12

D

11
13

SLOT-DEPENDENTCMDA,DATAREGISTERSELECT
AND D/A CONTROL

Writing to the Command A location controls the register
selection, auto sequencing, and global strobe updating of
the D/A converter in the analog output circuitry.

D/A control must precede any change in range register
data. This write resets the register auto-sequencing circuit
to the proper register. The lower four bits represent the
register to be written first. Bits D5 and D6 represent the last
channel for auto sequencing of the data written to the
output data registers (registers 0 through 7). Setting bit D7
enables global strobe (see below) to update analog outputs
simultaneously.

SLOT-DEPENDENT.CMDB, D/A DATA AND RANGE
DATA

Through the use of register auto sequencing, the various
D/A control registers can be filled by writing repeatedly to
the CMDB register. Range registers are filled first, in de­scending order from 3 to 0. After filling the range registers,
the DAC data bytes are written for each channel, LSB first.
The DAC requires two write operations to supply the 13
bits necessary for data and polarity information. The range
registers are only set once, until a write to CMDA points to
the range registers again, and thedata-registers are con­tinuously updated to allow variable output. When the
global strobe update feature is not enabled, the output
channel is automatically updated upon receipt of the sec­ond byte of data. When the global strobe update feature is
enabled, data is not latched into the conversion register of
the D/A converter until receipt of the global strobe signal.
Twelve of the available 16 registers are implemented in this

Circuitry.

COMMAND FUNCTION
CMDA None

CMDB None
Write Functions:
COMMAND FUNCTION
CMDA Data register select, D/A Control

CMDB
xxx9D

D/A Data and Range
Strobe (update all outputs)

AOM5-4

Initially, a D/A control is issued which must select one of
the four range registers, register 12,13,14, or 15 for channel
3, 2, 1, or 0 range, respectively. Additionally, the D/A
control must select the last channel for auto sequencing,
and either enable or disable the global strobe update fea­ture.

After the D/A control is issued, the D/A data is loaded.
The command circuitry selects the appropriate range reg­ister, and register control is relinquished to the auto-se­quencer. The range registers are filled with the proper
range data. The auto sequencer drops to the output data

AOM5

Analog Oufpuf Module

registers. D/A output data is written, and the sequencer
automatically “points to” the next register to be written.
The data is written LSB first, then MSB, going from chan­nel 0 to channel 1, then 2, then 3. If the global strobe update
feature is disabled (in the D/A control word) the output of
the D/A converter is updated immediately upon receipt of
the MSB of data (including the polarity bit). If the strobe
input is enabled, the data is not latched into the output
registers of the D/A converter until receipt of the active
low strobe input.

To determine the digital value corresponding to a given
voltage, it is necessary to know the output range setting of
the DAC. Since the AOM5’s 13-bit converters are organ­ized as 12 data bits plus sign bit, there are actually 4096
possible voltage levels to be programmed, specified with
digital values of O-4095. 13-bit resolution results from
setting the polarity bit for positive or negative output. The
full-scale value is the nominal full-scale value minus 1 LSB,
and the resolution is 1 part in 4096, or about 2.44mV on the
10 volt range. The DAC counts for a particular output can
be calculated as:

COUNTS = ABS [ ( VOLTS / RANGE ) x 4096 I

where counts = DAC data, volts = desired voltage output,
and range = the output range setting for the particular
channel. The digital data must be adjusted to include the
sign bit (the D7 bit in the MSB of the data). This may be
accomplished by adding 128 to the MSB if negative voltage
output is desired.

xxx9D (STROBE)
GLOBAL ANALOG OUTPUT UPDATE!

The strobe command is used to synchronously update all
analog output channels. Thestrobe feature is global, affect­ing all D/A channels in a system whose global strobe
feature has been enabled. Any analog output whose global
strobe has been enabled, and whose data has not been
changed since the last global strobe was issued, will not
change its output voltage.

Writing to the global strobe command location causes the
STROBE line to go active low, and allows global update of
all DAC outputs if the analog output circuit is so config­ured.

AOM5-5

AOMSA
Analog Output Module

DATA

CHANNEL 0

CHANNEL 1
CHANNEL 2
CHANNEL 3

MDA. STROBE

(WRITE ONLY) (WRITE ONLY)

CMDS, DATA/RANGE

CMDA (WRITE) D/A CONTROL

D7 D6 D5 D4 D3 D2 Di DO

CMDB (WRITE) D/A DATA OR RANGE
Data Register Format

MSB

D7 D6 D5 D4 D3 D2 Di DO

CHAN 0

CH3OUT-

a

RANGING

2v

IV

J

TO AID

MUX

Last channel for auto-sequencer
Global strobe: Enable (0), Disable (1)

LSB

D7 D6 D5 D4 D3 D2 Dl DO

/ I ’ L :X$+:2 bits

Range Register Format

D7 D6 D5 D4 D3 D2 Dl DO

I

I

‘igure 3. AOM5 Block Diagram and Register Funcfions

AOM5-6

Sign bit: Negative (i), Positive (0)

Range: 1OV (0), 5V (I), 2V (2), 1V (3)
Unused

CMDB WRITE REGISTER TABLE

REGISTER NUMBER

0

1

2
3

DISCRIPTION

Channel 0 LSB
Channel 0 MSB

Channel 1 LSB
Channel 1 MSB

COUNT SEQUENCE

-4-

:

----

+

I

:

----

-b

AOh4.5

Analog Output ModuZe

Last Channel = 0

Last Channel = 1

4
5

6
7

8
9
10

11

12
13
14
15

Channel 2 LSB
Channel 2 MSB

Channel 3 LSB
Channel 3 MSB

Not Used
Not Used
Not Used
Not Used

Channel 3 Range
Channel 2 Range
Channel 1 Range
Channel 0 Range

-+1

-+1

-+1

-+

Last Channel = 2

Last Channel = 3

1

L----b----

SROBE (WRITE) UPDATE OF OUTPUTS, ADDRESS = xxx9D

The GLOBAL STROBE can be used to simultaneously update all D/A outputs in the system. This includes all
output channels on all D/A cards in the system which have been programmed to respond to GLOBAL
STROBE.

To enable the AOM5 to respond to GLOBAL STROBE, write a 1 to bit 7 of the AOM5 CMDA register.

OUTPUT DATA

Calculate the data value (number of bits) for a desired output voltage as follows:

DATA VALUE = (ABSOLUTE VALUE (VOLTAGE) I RANGE) X 4096

Set bit 13 to 0 for positive output, or 1 for negative output. See CMDB for information on writing data to AOM5
data registers.

AOM5 BZock Diagram and Register Functions (Cont.)

AOM5-7