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AMM2
Master Analog Measurement Module
The AMM2 Analog Measurement Module combines three important Series 500 func-
tions into a single module. First, the AMM2 functions as a standard analog input
module, and wiu accept up to 16 single-ended or eight differential analog input signals.
It contains signal conditioning and switching circuitry for these channels. Second, the
AMM2 selects and conditions analog signals from other analog input modules in a
Series 500. Last, the AMM2 serves as a 16-bit A/D converter for its own analog input
channels, as well as any other analog signals which have been processed by the global
select/conditioning circuitry. After analog conditioning, signals are routed to the A/D
converter section of the module for the analog-to-digital conversion process.
Input signals are applied to the AMM2's analog input channels through on-card quick-
connect screw terminals. The AMM2 has a total of 16 local single-ended, or eight dif-
ferential inputs. The input configuration is controlled through software, rather than
with hardware switches. These analog input channels can be conditioned with pro-
grammable local gains of either xl or x10.
Global conditioning consists of a high-speed software-controlled gain amplifier with
programmable xl, x2, x5 and x10 gain values. All analog inputs connected to the Series
500 pass through the global circuitry, whether the signals originate on the AMM2 or
some other analog input module. Therefore, these gain values can be applied to any
analog input in the system.
For A/D conversion, the AMM2 uses a l&bit successive approximation converter. A
maximum conversion time of only 20psec allows sampling rates as high as 5OkHz. To
maximize resolution, the AMM2 has O-XIV and &lOV A/D converter ranges which are
software selectable.
CAUTION: Always tum off the system power before installing or removing modules.
To minimize the possibility of EM1 radiation, always operate the system with the top
cover in place and properly secured.
The Ah4M2 is designed to be used only in slot 1 of the 500-series system baseboard. To
install the module, first remove the baseboard top cover and install the module in slot 1
with the component side facing the power supply.
Document Number: 501-912-01Rev. C AMM2-1
Figure 1. AMM2 Component Layout
AMM2-2
High-speed Acquisition Mode with AMMP and ANINQ
(SOFT500 and QUICK500)
The ANINQ command can operate the AMM2 module in a high-speed "auto-acquire"
mode at an aggregate throughput rate of up to 5OkHz. Auto-acquire applies to single or
multiple channels. For multiple channels, the per-channel scan rate equals 5OkHz divid-
ed by the number of channels.
The analog input modules AIM2 and AIM3 can also provide up to 5OkHz throughput
when these modules are used in a system containing an AMM2.
To operate the AMM2 in auto-acquire mode, you must satisfy the following
requirements:
1. The analog input channels sampled by ANINQ may be on an AMM2, AIM2, or
AIM3.
2. All the channels sampled by the specific ANINQ command must be on one module.
3. If the input channels are on an AlM3, the AIM3 must be set to xl gain.
4. The AMM2's input filter must be set to lOOkI&.
If any of these conditions cannot be met, the speed of the ANINQ command will revert
to the speed of an ANIN command. Under these circumstances, it is better to use
ANIN in order to take advantage of foreground/background operating mode.
NOTE: The ANINQ command in Soft500 and Quick500 has been optimized for auto-
acquire (5OkHz) operation with the AMM2. If you attempt auto-acquire mode with
BASIC's PEEK/POKE, or the memory READ&VRlTE commands of other languages, you
may receive incorrect data. If you do not use Soft500 or Quick500, Keithley suggests
that you run the AMM2 only in "regular acquisition mode". This mode is described
under the heading "SELECT ACQUISITION MODE" later in this manual.
Self-calibration During "CALL INIT" (SOFT500 and QUICK500)
The AMM2 module performs a self-calibration each time a CALL INIT is issued.
Soft500 executes a CALL INIT each time it is run in the non-resident mode, or just
once when it is loaded into memory in resident mode. Quick500 executes a CALL INIT.
each time it is loaded under the QuickBASIC environment or with the "QRUN" option,
or just once when it is made resident with the "QLOAD" option. Therefore, you need
not issue a separate CALL INIT specifically to calibrate the Ah&I2.
Soft500 and Quick500 will expect an AMM2 in the system if the configuration file
(CONFIGTBL) shows an AMM2 in slot 1. If the software cannot complete the calibra-
tion, it will issue an error message such as "Unable to calibrate A/D module". If this oc-
curs, check that:
1. The Series 500 is turned on.
2. The cable between Series 500 and IBIN interface is connected.
3. An AMM2 is mounted in slot 1 of the Series 500.
AMM2-3
Connection and Operation
Signal Connection
The AMM2 can be programmed for either differential or single-ended local input con-
figurations. These local input signals are applied to screw terminals located toward the
rear portion of the AMM2. Single-ended and differential inputs use the same screw
terminals.
The channel numbers are shown in Figure 1. Figure 2 shows typical connections for
channels 0 through 7 in differential mode. For differential mode, connect the high (+)
side of an input signal to the (+) terminal, and the low (-) side of the signal to the
corresponding (-) terminal. When the AMM2 is configured for single-ended input,
connect the high (+) side of the input signal to one of the terminals 0 through 15, and
the low (-) side to the module ground at either end of the terminal strip. In Figure 2,
the numbers listed in parentheses above the lower connector are the single-ended local
channels 9 through 15.
.' ' ' ' `Jl" ' ' ' '
eeeeeeeee@
GND 7+ 6+ 5+ 4+ 3+ 2+ l+ Cj+GND
Measured
Voltage
" Shield
(Optional)
Series 500
Chassis Ground
t
I
1 I
Figure 2. Typical Differential Connection (Channel 0 Shown)
CAUTION: The AMM2 inputs are non-isolated. In single-ended mode, one side of the
input is connected to power line ground. Any signal connected to the AMM2 must
also be referenced to power line ground, or module or system damage may occur Also
note that inaccuracies on other channels may result. When used in differential mode,
the AMM2 local inputs must both be within flOV of module ground for proper
operation. If either signal exceeds k3OV module damage may result.
In many situations, shielded cable may be required to minimize EMI radiation, or to
keep noise to a minimum. If shielded cable is used, connect the shield to ground only,
and do not use the shield as a signal-carrying lead. Usually, a module ground terminal
should be used, but in some cases better results may be obtained by using one of the
baseboard ground posts. Use the configuration that results in the lowest noise.
For shielding to be effective, the shield must contain both high and low signal wires,
and must not carry any other signals. If a number of AMM2 signal input lines are
shielded, all shields should be connected to the same ground terminal.
Signal Conditioning
Figure 3 shows a simplified block diagram of the AMM2. The module is divided into
six general sections: a local multiplexer, a local programmable gain amplifier, a global
multiplexer, a global programmable gain amplifier, a programmable low-pass filter, and
a 16-bit A/D converter.
Local input signals from channels 0 to 15 are applied to the local multiplexer for selec-
tion. At any given time, only one channel will be selected, as determined by the
SELECT CHANN-S L command (covered later in this section). The signal from the
selected channel is then routed through a local programmable gain amplifier to the
global multiplexer for further signal selection and conditioning.
The globalmultiplexer se!ects a sing!e signal from among the 10 s!ots in the system. In
this manner, signals from any of the 10 slots can be selected by software. The global
multiplexer is controlled by the SELECT SLOT command, discussed later in this
section.
After the signal is selected, the Global PGA applies software-selectable gains of xl, x2,
x5, or x10. The signal finally passes through a one-pole filter with software selectable
-3db frequencies of either lOOkHz or 2kHz. When this signal conditioning process is
complete, the signal is routed to the 16-bit A/D converter for digitization. After the con-
version process, digital data representing the applied signal travels via the baseboard
and interface card to the host computer.
Local
Programmable
Gain Amplifer
(Xl orX10) Global
16 Single-ended or Programmable
8 Differential -7 Gain Amplifier
inputs (Xl .XZ,X6,OR
(input Mode
Programmably
16Bl-r E
Selected) \L AlDAND =
SM-
Analog hyd.S f
Programmable
Locd From Other Programmable
Slots e- Filter
Channel
(1OOkHz OR
2kHz)
Figure 3. AMM2 Signal Conditioning
Input Filtering
Noise introduced into the input signal can corrupt the accuracy of the measurement.
Such noise will usually be seen as an unsteady reading, or, in some cases, as a con-
stant offset. In the former case, the effects of noise will usually be quite obvious, but
may not be noticeable in the steady-state offset situation.
Frequently, noise is introduced into the signal from 50 to 6OHz power sources. In many
cases, noise can be attenuated by shielding or relocating the input signal lines, as
discussed earlier. It may also be possible to reject unwanted 60Hz noise by using the
AMM2-5
AMM2 in differential mode. Since the 6OHz noise may also be present on the low side
of the signal, the differential amplifier will reject the common signal. In more difficult
situations, however, it may be necessary to filter the input signal to achieve the
necessary noise reduction. This is especially important to make good use of 16-bit A/D
resolution.
When noise is a problem, a single-pole low-pass filter like the one shown in Figure 4
can be connected between the input signal and the corresponding AMM2 channel.
Note that the filter is made up of a single capacitor and resistor with the capacitor con-
nected between the AMM2 channel input terminal and the module ground terminal.
The resistor is then placed in series with the high input signal lead.
From Signal To AMM2 Input
Figure 4. Input Filtering
A common reference point for a simple filter like the one in Figure 4 is the -3dB or
half-power point, which is given as follows:
f-m = 1/(27rRC)
where f is in Hz, C is in farads, R is in ohms. Above this frequency, filter response will
roll off (decrease) at a rate of -20dB per decade. Thus, each time the frequency in-
creases by a factor of 10, filter output voltage decreases by a factor of 10 (-20dB).
Although such filtering can quiet down a noisy signal, there is a trade-off in the form
of slower response. This response time may be important in the case of a rapidly
changing input signal. For the filter in Figure 4, the response time to 1% of final value
is 4.6RC, while the response times to 0.1% and 0.01% of fmal value are 6.9RC and
9.2RC, respectively.
As an example, assume that 10 counts of 6OHz noise is present in the input signal. To
reduce the noise to one count, an attenuation factor of 10 (-20dB) at 6OHz will be
necessary. Thus, the filter should have a -3dB point of 6Hz.
To determine the relative RC values, the above equations can be rearranged to solve for
either R or C. If we wish to choose a nominal capacitor value and then solve for the
resistance, we have:
R = 1/(2&f-,,,)
AMM2-6
Choosing a nominal value of 2pF for C, the necessary resistance is:
R = 1427r x (2 x 10") x 6Hz)
R = 13.263k
The resulting response times with these R and C values would be:
t(l%) = 4.6RC = 122ms
t(O.l%) = 6.9RC = 183ms
t(O.Ol%) = 9.2RC = 244ms
Current-to-Voltage Conversion
AMM2 local inputs are designed to accept voltages in the range of &lOV. Thus, the
AMM2 can be directly connected to many signal sources. Some transducers and in-
strumentation, however, provide current outputs that must be converted into voltages in
order to be measured through an AMM2 input channel.
When connecting current inputs to the AMM2, a resistor should be installed across the
input to make the necessary current-to-voltage conversion. J4, J5, and J6 provide loca-
tions for installing these resistors on the AMh42. Refer to the circuit schematic and
board layout diagrams for header information.
The value of the resistor can be determined from Ohms law as follows:
R = E/I
Where R is the resistance in ohms, E is the maximum desired voltage in volts (usually
the upper range limit of the AID converter), and I is the maximum anticipated current
in amps.
As an example, assume the AID converter range is zero to +lOV and that the expected
current lies in the range of four to 401~~4.The required resistance is:
R = 10/0.04
R = 250
Thus, a 25OQresistor should be installed across the input of the channel in question
(note that a 2508 value is required when using Soft500 engineering units conversion).
Since current measurement accuracy is directly related to the accuracy of the resistor,
use the smallest tolerance resistor available (typically 0.1%). Suitable 25OQprecision
resistors can be purchased from Dale Resistors, (PIN RN55E2500B), or from Keithley
(PIN 500-RES-250).
AMh42-7
Analog-to-Digital Converter Timing
When programming high-speed sampling sequences, certain timing constraints concern-
ing the AID conversion cycle should be observed. Depending on the AMM2's acquire
mode, the scenario for receiving converted values from the A/D is very different. Refer
to the discussion of the acquire modes below for specific instruction on how to process
analog signals.
To increase system throughput, data latches have been provided on the AMM2, making
data from the last conversion available while the converter is busy processing another
reading. The data is refreshed (updated) every time a conversion has been completed.
External Trigger Operation
The AMM2 has the capability of triggering an acquisition from an external TTLlevel
source. The jumper on the Ah4M2 (J3) dictates the triggering source. The external trig-
ger can only be used in 5OkHz auto acquire mode which is explained below in the SET
ACQUISITION MODE command discussion.
When the AMM2 is in 5OkHz auto acquire mode, the trigger source can be set to either
external or internal by the J3 jumper. When set for internal triggering, the AMh42 con-
tinuously converts analog signals as described below in the SET ACQUISITION MODE
command discussion. When the J3 jumper is removed, a TI'Llevel signal can be attach-
ed to pin 2 of the jumper header. A low level applied to pin 2 will enable the con-
tinuous conversion process, a high level applied to pin 2 will suspend the continuous
conversion process. In either case, the application program must synchronize itself to
the conversion process by polling the conversion status as explained in the SELECT AC-
QUISITION MODE command discussion.
The pin configuration of the jumper header is as follows:
pin 1 +5v
pin 2 trigger input
pin 3 OV (ground)
The J3 jumper should be across pins 2 and 3 for internal trigger operation. The jumper
should be removed and the external trigger source should be connected to pin 2 for ex-
ternal trigger operation
Commands
Table 1 summarizes the commands used with the AMM2. Note that several commands
share the CMDA and CMDB locations. Some commands use only selected bits in the
command byte, others are differentiated by whether a read or write operation is
performed.
Table 1. Commands Used with the AMM2
Command Address Signal Line Bits Used
SELECT CHANNEL xxx80 CMDA (Write) DO-D3
SELECT LOCAL CHANNEL MODE xxx80 CMDA (Write) D4
SELECT LOCAL GAIN xxx80 CMDA (Write) D5
SELECT ACQUISITION MODE x=80 CMDA (Write) D6
SELECT FILTER xxx80 CMDA (Write) D7
SELECT SLOT xxx81 CMDB (Write) DO-D3
SELECT CMDA READ MODE xxx81 CMDB (Write) D4
SELECT RANGE xxx81 CMDB (Write) D5
SELECT GLOBAL GAIN XXX81 CMDB (Write) D6-D7
RESET AND RECAL XXX9A CMDC (Write) ALL
A/D LOW DATA! xxx80 CMDA (Read) ALL
A/D STATUS* xxx80 CMDA (Read) ALL
A/D HIGH DATA xxx81 CMDB (Read) ALL
A/D START xxx9B CMDD (Write) ALL
EOC (end-of-conversion) STATUS XXX9B CMDD (Read) ALL
* The information read from CMDA is selected by the SELECT CMDA READ MODE
command. Refer to the sections below for the full description of their operations.
The "xxx" in the address column signifies the three hexidecimal digits that make up the
base hardware address which is either switch selected or programmed on the interface
card. The suggested address is &HCFFBO, so "xxx" = "&HCFF".
Select Channel, Local Gain, Filter, Acquisition Mode, and Channel Mode.
D5 D4 D3 D21 Dl DO
I
Channel Select: SE (O-15), DIFF (O-7)
Channel Mode: Single-ended (l), DIFF (0)
Local Gain: Xl (0), X10 (1)
ACQ Mode: 50kHz Auto Acquire (l), Regular Acquire (0)
Filter Mode: 1OOkHz (0), 2kHz (1)
Figure 5. CMDA Write Format (Address xxx80)
AMM2-9
Select Slot, Range, Global Gain, and CMDA Read Mode.
D71D6 1D5 1D4jD3 D2( Di ID0 Byte Format
Select Slot: (O-15)
CMDA Read Mode: A/D Status (0), Low Data (1)
Select Range: -1 OV +l OV (l), 0 Cl OV (0)
Select Global Gain: Xl (0), X2 (l), X5 (2), X10 (3)
Figure 6. CMDB Write Format (Address xxx81)
SELECT CHANNEL
Location: xxx80
The SELECT. CHANNEL command is used to control the local signal multiplexer on the
AMM2, thus determinin g which of the local input channels is selected for A/D conver-
sion. This command affects only those signals connected to the AMM2 local inputs,
and does not affect input channels connected to modules located in other slots.
SELECT CHANNEL must be used in conjunction with the SELECT SLOT command to
select the channels on slot one of the chassis.
Note that the channel number occupies the least significant four bits of Ch4DA. Make
sure that the channel number is combined with the appropriate upper four bits, as
shown in Figure 5, before it is sent.
SELECT LOCAL CHANNEL MODE
Location: xxx80
The SELECT LOCAL CHANNEL MODE command controls the configuration of the
local input channels on the AMM2. The AMM2 input channels can be configured as
either 16 single-ended or eight differential input channels. This command is selected by
assigning a value to the D4 bit position of CMDA as shown in Figure 5. A value of 1
will set the inputs to single-ended, a value of 0 will set them to differential.
Make sure that the other bits in the CMDA byte represent the desired selections before
it is sent.
SELECT LOCAL GAIN
Location: xxx80
The gain applied to the local channels of the Ah&I2 is programmable and can be set by
assigning a value to bit position D5 in CMDA. As shown in Figure 5, a value of 0 will
apply a local gain of Xl and a value of 1 will apply a local gain of X10 to the AMM2 in-
put channels.
AMM2-10
The local gain can be changed at any time as long as the channel settling time is
satisfied before the conversion is started.
Make sure that the other bits in the CMDA byte represent the desired selections before
it is sent.
SELECT ACQUISITION MODE
The AMM2 has the capability of operating in either of two modes; the regular acquisi-
tion mode, and the 5OkHz auto acquisition mode. As shown in Figure 5, the acquisition
mode is set by assigning a value to bit position D6 in CMDA. Assigning a value of 0
enables regular acquisition mode, a value of 1 enables 5OkHz auto acquisition mode.
To acquire an analog reading when in the regular acquisition mode, the slot, channel,
and gain must be selected. Then, after the appropriate settling time, the AMM2 is
issued a START CONVERSION command. At this time, the AMM2 latches the signal
and starts the digitization process. The EOC STATUS command can be polled for end-
of-conversion (EOC) after which the digitized value can be read. The conversion process
will consume approximately 20psec.
Since the incoming signal is latched when the START CONVERSION command is
issued, the slot, channel, and gain selections can be changed immediately after the
command is issued. This will allow the settling time for the new selections to be
satisfied concurrently with the conversion of the previous selection. This type of opera-
tion is not required but will increase the throughput capability of regular acquisition
mode.
The 5OkHz auto acquisition mode allows full 50kHz acquisition speed on analog signals.
Upon placing the AMM2 in this mode, the A/D enters a free-running 5OkHz conversion
process. Do not attempt to issue the START CONVERSION command in this mode.
Some microcomputers may not be capable of keeping up with the AMM2 in auto ac-
quire mode. If the AMM2 out-paces your microcomputer, the data points will be
unreliable.
After the completion of a conversion, the AMM2 begins the next conversion immediate-
ly. The EOC STATUS command can be used to synchonize your program with the con-
versions. The conversions will take place on the slot and channel that are presently
selected at a rate of 5OkHz. The conversion status bit will be reset by the reading of
either the high or low AID data bytes. Figure 7 shows the timing for single channel
auto acquire operation.
While in auto acquire mode, the EOC status bit will become true (low) after the first
A/D conversion. Even though the next conversion begins immediately, the status bit re-
mains true until the AID data is read. If the data is not read, it is over-written.
AM.M2-ll
EOC Status
Bit (CMDD)
Poll EOC
Bit Status (CMDD)
Read Low
Byte
Completed
Figure 7. Single Channel Auto Acquire Timing
Fiie 8 shows an example of the EOC status being polled only after one or more con-
versions have taken place. Even though the EOC status bit indicates that the conversion
is complete, there is no way of telling if another conversion is about to be completed.
Trying to read the data while the latches are being updated will cause unreliable
results. To guarantee reliable readings, your program should synchronize itself with the
AMM2 by taking a dummy reading to clear the conversion status bit. The next time the
status bit indicates the end of a conversion, the data at the AID latch will be valid for
the full 20psec.
1st 2nd 3rd
Conversion Conversion Conversion
EOC Status -H k J
Bit (CMDD) It- \-
I t
I
Poll EOC : L\
Bit Status (CMDD) , t Data in the ND
I I Latch is Updated Here.
Although the converter status indicates The EOC zatus bit
a completed conversion here, reading the data remains low until the
might be coicident with an update of the High or Low data are read.
data from the converter.
Figure 8. Polling the Status Bit After One or More Conversions
For multichannel auto acquisition operation, all of the settling times for the new chan-
nel must be satisfied 4psec before the EOC takes place. If it is not settled, it may be
necessary to throw away a reading or two until it has settled. To maximize the available
settling time, it is recommended that slot selection, gain selection, and channel selec-
tion take place directly after the EOC becomes true.
For optimum operation follow these steps:
1. Monitor the EOC status bit until an end-of-conversion is sensed.
2. Select a new gain, a new slot, and a new channel, as needed.
3. Read the latched data from the last conversion.
A timing diagram for multichannel operation is shown in Figure 9.
AMM2-12
EOC Status
I 4lq4- i I
Bit (CMDD) I
I
Poll EOC
Bit Status (CMDD)
Gain
Select lot mux
Slot + -I settling time : T
Select
- *,f-+
Channel
Select
Read Low
Byte
Read High
Byte
Set up
for Channel
B \ C Read
Channel Read Channel Channel
A Data Ready Channel I3 Data Ready B
A
Figure 9. Multichannel Operation in Auto Acquire Mode
Even though the AMM2 is capable of digitizing analog signals at 50kHz, some modules
in the Series 500 module library are not capable of settling at these speeds. When do-
ing multichannel acquisition, consult the individual module's hardware manual for ap-
propriate settling times.
SELECT FILTER
Location: xxx80
Two filters are available in the AMM2; a 1OOkHzfilter, and a 2kHz filter. These filters
restrict the bandwidth of the incoming signal, rejecting either noise or unwanted high
frequency components that may create aliasing.
It is desirable to reject all signal frequency components that are greater than l/2 the
sampling frequency. These frequency components cause aliasing which produces inac-
curate waveform representation. The filters are designed to reject frequencies above
1oOkHz or above 2kHz, depending on the filter used. The 1OOkHzfilter, while not pro-
viding complete protection against aliasing, does reduce the system noise with a
minimal effect on settling time.
Assign a value of 0 to bit position D7 in CMDA to select the 1OOkHzfilter, assign a
value of 1 to select the 2kHz filter.
Make sure that the other bits in the CMDA byte represent the desired selection before
it is sent.
AMM2-13
SELECT SLOT
Location: xxx81
The SELECT SLOT command controls the global multiplexer on the AMM2, selecting
the appropriate slot on the Series 500 baseboard from which to read the input channel.
The value to be written to the SELECT SLOT location occupies the four least significant
binary digits of the command. Make sure that the channel number is combined with
the appropriate upper four bits as shown in Figure 6 before it is sent.
As indicated in Table 2, there are other values besides slot numbers that can be written
to this location. These values select ground, +5V, and +%JVsources and are intended
primarily for diagnostic purposes.
Table 2. Values Written to the SELECT SUrr Location
Function Binary
Ground (0 volts) bbbbOOO0
Slot 1 bbbbOOO1
Slot 2 bbbbOOl0
Slot 3 bbbbOOl1
Slot 4 bbbbOlO0
Slot 5 bbbbOlO1
Slot 6 bbbbOll0
Slot 7 bbbbOll1
Slot 8 bbbblOO0
Slot 9 bbbblOO1
Slot 10 bbbblOl0
Reserved bbbblOl1
Reserved bbbbllO0
+lOV Reference bbbbllO1
Ground (0 volts) bbbblll0
+5V Digital Power Supply bbbbllll
SELECT CMDA READ MODE
Location: xxx81
This command selects the usage of the CMDA read. Two types of information can be
read from CMDA (note that this affects only the read operation of CMDA), these are,
the low data byte of the AID or the AID status. In the low data byte mode, CMDA sup-
plies the low data byte of the AID readings. In the AID status mode, CMDA supplies
status directly from the AID. The AID status is described further in the sections below.
NOTE: When the CMDA read mode is set to AID status, a reset and recal sequence
will be initiated by any start conversion command. The start conversion command can
come either from a write to CMDD, or from the auto acquire mode hardware if this
mode has been enabled by a value of 1 in bit position D6 of CMDA. To avoid acciden-
tally initiating a reset and recal sequence, be sure bit position D6 of CMDA is set to a
value of 0 before changing the CMDA read mode to A/D status. Do not write to CMDD
or change D6 of CMDA to a value of 1 as long as the CMDA read mode is set to A/D
status.
AMM2-14
Assign a value of 0 to bit position D4 in CMDB to read A/D status from CMDA, assign
it a value of 1 to read the A/D low data byte.
Make sure that this bit is combined with the other appropriate bits as shown in Figure
6 before it is sent.
SELECT RANGE
Location: xxx81
The AMM2 has two programmable ranges; flOV (bipolar lOV) and zero to +lOV
(unipolar 1OV). Assigning a value of 0 to bit position D5 in CMDB will select the
AMM2 unipolar 1OVrange, assigning a value of 1 will select the bipolar lOV range.
Make sure that this bit is combined with the other appropriate bits as shown in Figure
6 before it is sent.
SELECT GLOBAL GAIN
Location: xxx81
The GLOBAL GAIN command controls the PGA (Programmable Gain Amplifier)
located on the AMM2 module. Since all analog inputs are processed by the PGA, the
GLOBAL GAIN command affects every analog input connected to the Series 500. This
command is issued in combination with other commands on CMDB. The GLOBAL
GAIN value occupies the two most significant bits of CMDB and must be combined
with the other bits of the CMDB byte before it is issued.
Four programmable gain values, xl, x2, x5, and x10, are available with the PGA. These
gains are selected by setting the appropriate bits in CMDB before it is issued.
Table 3. Values Written to the GLOBAL GAIN Location
PGA Gain Binary
xl OObbbbbb
x2 Olbbbbbb
x5 lobbbbbb
Xl0 llbbbbbb
RESET AND RECAL
Location: xxx9A
The RESET AND RECAL command starts the internal A/D calibration process. The pro-
cess takes approximately 360msec and should be completed once every time the system
is powered up.
After issuing this command, wait at least 36Omsecbefore any conversions are attemp-
ted. To make sure that the calibration has taken place, set the CMDA read-mode to AID
AMhO-
status, as described above. The bit configuration of the calibration status is described
below. This bit can be polled to make sure calibration has been completed.
This command has no specific data associated with it, any value sent will start the
calibration process.
AID LOW DATA - AID STATUS
Location: xxx80
The contents of CMDA depends on the state of the AMM2 set by the SELECT CMDA
READ MODE command. If D4 of CMDB has been set to 0, CMDA returns the A/D
status of the AMM2. If D4 has been set to 1, the low byte of the AID counts is return-
ed in CMDA.
When AMM2 is in the A/D status mode, the bit configuration of the CMDA byte is as
follows:
DO none
Dl none
D2 none
D3 none
D4 none
D5 TRACKING (lstracking in process, O=tracking stopped)
D6 CONVERTING (l=conversion in process, O=no conversion in process)
D7 CALIBRATING (l=calibration in process, O=calibration not in process)
After the A/D completes a digitization of an analog signal, it begins a process called
tracking. The A/D consumes 4,usecfor the analog signal at its input to be tracked to the
specified accuracy. The time relationship between the TRACKING bit and the EOC bit
in CMDD is shown in Figure 10.
The converting bit indicates the actual A/D conversion status. The time relationship bet-
ween the CONVERTING bit and the EOC bit in CMDD is shown in Figure 10.
Won't Reset Until
bata is Read
EOC Bit
in CMDD
Tracking Bit
in CMDA
Converting Bit i c-- 16~s
in CMDA 47K Conversion
Begins
Figure 10. Time Relationship of Status Bits
The CALIBRATING bit returns the status of a RESET AND RECAL command as
described above.
AMM2-16
If the M2 is in the low data mode, the byte received is the low byte of the 16 bit
A/D conversion. Since the module incorporates data latches, one conversion may be
read while another conversion is in progress. To find out when data from one conver-
sion is available, use the A/D STARTlEOC S'IXI'US command, discussed below.
Reading this location resets the EOC status.
AID HIGH DATA
Location: xxx81
The A/D HIGH DATA command performs essentially the same function as the A/D
LOW DATA command, except that the high data byte is returned. Since the Alvilvl2 has
a 16 bit A/D, all of the bits in the high data byte are significant.
Once both the low and the high data bytes have been obtained, the total number of
counts representing A/D converter data can be determined with the following BASIC
formula:
co = DL + 256*DH
CO represents the number of counts, and DL and DH are the low and high bytes
respectively. Since the AMM2 uses a 16-bit converter, the number of counts will lie in
the range of zero to 65,535.
Reading this location resets the EOC status.
A/D START
Location: xxx9B
The A/D START COMMAND starts the A/D conversion process. Writing to the A/D
START location will trigger (start) the A/D conversion cycle. Although any value (O-255)
can be written to trigger a conversion, a value of 255 should be used to minimize noise.
Do not issue an A/D start command while in auto acquisition mode or the internal tim-
ing of the A/D will be skewed.
The A/D conversion cycle takes approximately 16psec. During this period, the converter
should not be re-triggered. Status of the conversion process can be checked by access-
ing the EOC STATUS command.
EOC STATUS
The EOC S'MTUS command returns a byte of data which indicates the state of the con-
version process. The returned value will depend on whether a conversion has been
completed (see Table 4).
AMM2-17
Table 4. Values Read from the A/D START/STATUS I-ocation
EOC Status Binary
Conversion in process l.XXXXXXX
End-of-conversion OXXXXXXX
Calibmtion
This section contains calibration procedures for the AMM2 module. Note that these
procedures are intended for the field and may not be as accurate as those used in the
factory. Calibration accuracy depends both on the accuracy of the equipment used in
the procedure as well as the skill of the individual. If you are not familiar with calibra-
tion equipment, do not attempt AMM2 calibration.
This procedure presumes that the unit is in working condition and at least one factory
calibration has been done in the past. An additional procedure is necessary to select
R25, R26, R27 and R28 if the voltage reference Ul3 has been replaced. The procedure
for replacing Ul3 is described after the section on troubleshooting.
Environmental Conditions
Calibration should be performed at an ambient temperature of 23