| Signal Name | Type | Description |
| COM0± (one wire)COM<0..3>± (two wire)COM<0..1>A±(four wire) COM<0..1>B± (four wire) | Input/Output | Common---The common for each bank. |
| CH<0..47> (one wire)CH<0..23>± (two wire)CH<0..11>A± (four wire)CH<0..11>B± (four wire) | Input/Output | Channels---Where signals are connected to the switch card. CHx+ and CHx- are switched together. |
| 1WireLoRef | Input/Output | 1 Wire Low Reference---The common reference signal used in one-wire mode. |
| TRG-IN | Input | Trigger Input---Trigger from an instrument to advance the switch card to the next scan entry. |
| S_ADV | Output | Scanner Advanced---Trigger to an instrument that indicated the switch card has advanced to the next scan and relays are debounced. |
| SHDNn | Input | Emergency Shutdown---The trigger used to shutdown the system. |
| +5V OUT | Output | +5V VDC Source---Provide +5 power pin. |
| GND | Output | Ground---Provide system ground pin. |
| COM0± (one wire)COM<0..3>± (two wire)COM<0..1>A±(four wire)COM<0..1>B± (four wire) | Input/Output | Common---The common for each bank. |
| CH<0..47> (one wire)CH<0..23>± (two wire)CH<0..11>A± (four wire)CH<0..11>B± (four wire) | Input/Output | Channels---Where signals are connected to the switch card. CHx+ and CHx- are switched together |
Table 4: Pin Description
# 3.3 TB-6221 Terminal Board
Users can use the TB-6221 terminal board that consists of a printed circuit with screw terminals. The terminal block connects directly to the front panel I/O connector of the PXI-7921.
The TB-6221’s default printed circuit is in 2-wire mode. If other configuration is preferred, user can refer the table on TB-6221 to identify the pin connected.
# 2-wire MUX
This configuration has one 24x1 2-wire multiplexer Bank0, which has twentyfour channels. The following diagram illustrates the terminal board pin definition.
Figure 3: 24x1 MUX
# 2-wire, 2-group MUX
This configuration has two 12x1 2-wire multiplexers Bank0 and Bank1, each has twelve channels. The following diagram illustrates the terminal board pin definition.
Figure 4: Two 12x1 MUX
# 2-wire, 4-group MUX
This configuration has four 6x1 2-wire multiplexers Bank0, Bank1, Bank2 and Bank3, each has six channels. The following diagram illustrates the terminal board pin definition.
Figure 5: Four 6x1 MUX
# 1-wire MUX
This configuration has one 48x1 1-wire multiplexer Bank0, which has fortyeight channels. The following diagram illustrates the terminal board pin definition.
Figure 6: 48x1 MUX
# 4-wire MUX
This configuration has one 12x1 4-wire multiplexer Bank0, which has twelve channels. The following diagram illustrates the terminal board pin definition.
Figure 6: 4-wire MUX
# 4
# Operation Theorem
# 4.1 Hardware Block Diagram
The ADLINK PXI Switch Module features an onboard FPGA for relay switching control, trigger control, scanlist storage and sequencing. The PXI triggering and synchronization functions, such as Star Trigger and Trigger Bus are also supported. In addition to the Trigger In and Scanner Advanced signals for external instruments handshaking, the switch module provides eight channels of programmable digital I/O interface to facilitate general purpose control applications.
To make full use of the flexible trigger and signaling system on the PXI platform, the switch module has a built-in signal routing matrix that can exchange signals between front panel digital I/O, Star Trigger, and Trigger Bus.
Figure 7: Hardware Block Diagram
# 4.2 Operation Mode
The ADLINK PXI Switch Module provides two relay operation modes to accommodate different application requirements.
# Direct-update
The Switch Module updates the relay pattern immediately upon receiving a software command. This mode provides a straightforward control over switch module with minimal hardware intervention. If relay contact bouncing is of a concern, users would need to insert software delay.
ADLINK recommends the debounce time to be at least 5ms on PXI-7921.
# Auto-scan
The ADLINK PXI switch module features onboard memory to store user specified scanlist of up to 1024-entry. In each scanlist entry, users can specify relay pattern, pattern advancing delay time and criterion.
The switch module can set status bit or generate local interrupt to inform user’s program whether the pattern has been debounced and advanced to the next scanlist entry. Users can also specify one-time or cyclic scanning of scanlist entries.
This operating mode supports trigger signals for instrument handshaking. For more information on handshaking signals, please refer to section 4.3.
# 4.3 Handshaking
In the Auto-scan mode, ADLINK PXI switch module accepts Trigger In and generates Scanner Advanced signal to synchronize relay switching and measurements with PXI instruments or external measurement devices.
# Trigger In
The Trigger In signal from PXI instruments or external measurement devices instruct the ADLINK PXI switch module to update the relay pattern according to the one specified in the scanlist entry.
Users may specify wait-for-trigger instruction in a scanlist entry, to have the switch module wait for the Trigger In before relay pattern is updated. The polarity of Trigger In can be set to either rising-edge or falling-edge active.
For more information on scanlist configuration, please refer to the software programming users’ guide.
Figure 8 illustrates the available signal sources for the Trigger In signal. Signal names in the solid-line box represent the external (physical) signal on
connectors, and signals in the dotted-line box represents switch module’s internal signal.
Figure 8: Available signal sources for Trigger In
# Scanner Advanced
After updating the relay pattern, the switch module starts its debounce timer and waits for the relay contacts to settle. When the debounce time elapses, the switch module will generate a Scanner Advanced signal to notify the PXI instruments or external measurement devices that the relay contacts have settled, and ready to take a new measurement.
The waveform, polarity and pulse width of Scanner Advanced signal can also be software programmed.
For more information on scanlist configuration, please refer to the software programming users’ guide.
Figure 9 illustrates the available signal destinations for the Scanner Advanced signal. Signal names in the solid-line boxes represent the external (physical) signal on connectors, while signals in the dotted-line boxes represent switch module’s internal signal.
Figure 9: Available signal destinations for Scanner Advanced
# Handshaking protocol
Figures 10 and 11 depict the relationship between Trigger In, Scanner Advanced, and relay pattern in handshaking mode. In Figure 11 the Scanner Advanced is set to pulsating mode.
Figure 10: Handshaking operation (Scanner Advanced set in pulsating mode)
Figure 11: Handshaking operation (Scanner Advanced set in toggling mode)
Once the operation starts and has received a Trigger In signal, the switch module updates the relay pattern to that specified in the first entry of scanlist.
TS is the default debounce time for a switch module, i.e. 5ms for PXI-7921. TAn is the user specified scan delay time in the scanlist entry, indicating the time between the relay being debounced and the exact moment that a measurement device takes a new measurement. The actual delay time would be the greater of the two times, to guarantee that measurement devices take measurements after the signal path is fully settled, and the relays switch as close as possible to their maximum operating speed.
As the scan delay time elapses, the switch module generates Scanner Advanced signal to inform the measurement device to take a new measurement.
After the measurement completes, the measurement device will generate another Trigger In signal to have the switch module update the relay pattern to that specified in the second entry of scanlist.
The handshaking process will continue, until it reaches the end of the scanlist (if one-time scanning mode is selected), or when a software scan-abort command is received.
# Connecting, Trigger and Synchronize with External DMM
In this example, Agilent® 33401A 6-1/2 Digital Multimeter (DMM) is used to demonstrate signal connection for handshaking operation.
The DMM provides two terminals on the rear panel for the handshaking operation process, Trig In and VM Comp. The Trig In connects to the Scanner Advanced output on switch module, while the VM Comp to Trigger In. If the terminal board is used, wire Trig In to TRG\_IN on terminal board, and the VM Comp to S\_ADV.
Follow the instructions below to ensure the handshake functions properly:
1. Configure ADLINK PXI switch module’s Trigger In to rising-edge triggered, Scanner Advanced output in active-low pulsating mode with pulse width of at least 2us.
2. Configure the DMM to wait for external Trig In before a measurement, and generate VM Comp after a measurement. Arm the DMM to wait for the first trigger.
3. Setup the scanlist and auto-scan mode. The first entry in the scanlist should be set disable wait for the Trigger In, but enable Scanner Advanced output. Succeeding entries should enable both Trigger In and Scanner Advanced output. Download the scanlist to the switch module afterward.
4. Start auto-scan by sending scan start command to the switch module.
Figure 12: Signal Connection between Switch Module and Agilent DMM
For more information on scanlist configuration, scan mode setup, start, and stop functions of the auto-scanning process, please refer to the software programming users’ guide.
# 4.4 Trigger Bus
PXI specification defines eight bused-lines across slots in a segment. Users can route various trigger signal to synchronize multiple PXI instruments, and/or simplify field wiring across multiple ADLINK Switch Modules.
On ADLINK Switch Modules, the trigger bus driver is disconnected from PXI trigger bus before users’ configuration.
Figure 13 illustrates the available signal destinations for Trigger Bus[7..0]. Signal names in the solid-line boxes represent the external (physical) signals on connectors while signals in the dotted-line boxes represent the switch module’s internal signal.
Figure 13: Available signal sources for Trigger Bus[7..0]
# 4.5 Auxiliary Digital I/O
The eight auxiliary digital I/O lines on ADLINK Switch Modules provide versatility to users’ control applications. Each digital I/O line can be input, output or tri-stated. When in output mode, users can still read back the actual logiclevel on the I/O line. All digital lines are pulled-up to 5V with 10k ohm input resistance.
Note that AUX[2..0] are dual function pins, driving these pins while enabling handshaking or emergency shutdown functions, may falsely trigger the Switch Module or external instruments.
Figure 11: Auxiliary Digital I/O Function Block
# 4.6 Hot-Swap
The Switch Module can be hot-swapped during hardware failure in noninterruptible or high-availability systems where system shutdown is not an option.
PXI-7921 incorporates an onboard hot-swap control mechanism. However the extent of the hot-swap functionality support depends on the operating system and the PXI platform.
Microsoft Embedded $\mathsf { X P } ^ { \circledast }$ supports the native hot-swap function. The operating system automatically releases system resources when a switch module is extracted and recognizes the new device.
To remove a switch module, first release the screws on the front panel then push down the red latch on the ejector. When the blue LED turns on, the Switch module is ready to be removed by fully pushing down the ejector.
To insert another switch module, align the module’s edge with the card guide in the PXI chassis. Slide the switch module into the chassis, until there is resistance from the PXI connector. Push the ejector up and fully insert the switch module into the chassis, a click should be heard from the ejector latch. The blue LED on the front panel of the switch module will switch off when it is ready for operation. Tighten the screws on the front panel.
Note: Microsoft Windows $2 0 0 0 ^ { \circledast }$ does not natively support hot-swap however, PXI-7921 can be hot-swapped by manual control via an additional hot-swap driver. For the hot-swap driver on Windows 2000 and other operating systems such as Linux, VxWorks, etc., please contact ADLINK for more information.
# 4.7 Emergency Shutdown
In safety-critical applications, users can enable the emergency shutdown function on PXI Switch Module, to manually set the relay pattern to preset state.
To access this function, users must first configure the emergency shutdown function by windows API. Generally the trigger source is on the front panel and connected to a push button, which pulls the SHDNn pin to logic-low when activated. When multiple PXI Switch modules are installed in a PXI chassis, the trigger source can be routed through the PXI Trigger Bus and eliminate field wiring across multiple devices. Figure 12 illustrates available trigger sources for emergency shutdown. Signal names in the solid-line boxes represent the external (physical) signal on connectors and signals in the dotted-line boxes represent the switch module’s internal signal.
Figure 12: Available trigger sources for emergency shutdown
The default relay pattern for emergency shutdown is All-Off on PXI-7921; users can change the pattern by Windows API.
Upon receiving the emergency shutdown trigger, the Switch Module enters shutdown mode, and the relay pattern is switched to the preset state. If the Switch Module is in Auto-scan mode, the updating process would be stopped immediately; in Direct Update mode where the switch module will not accept any further update instructions.
To leave emergency shutdown mode, users must call adlSwitch\_Recovery in Windows API. The relay pattern would stay the same as they would in the emergency shutdown mode, and the scanlist (if set) being rewound to the first entry.
Note the auxiliary digital I/O function pin AUX2 shares the SHDNn pin; driving AUX2 to logic-low while the emergency shutdown function is enabled. It will falsely trigger the Switch Module to enter shutdown mode.
This function is disabled by default. For more information, please refer to the software programming users’ guide.
# 4.8 Watchdog Timer
In safety-critical applications, users can enable the watchdog timer function on PXI Switch Module to automatically set the relay pattern to preset state, in case the operating system or PXI controller crashes.
To access this function, users must first configure the watchdog timer overflow trigger source by windows API. Generally the trigger source would come from the onboard 32-bit watchdog timer. When multiple ADLINK PXI Switch modules are installed in a PXI chassis, the trigger source can be routed through the PXI Trigger Bus and eliminate redundant watchdog timer setting on multiple devices.
Figure 13 illustrates the available trigger sources for watchdog timer overflow. Signal names in the solid-line boxes represent the external (physical) signal on connectors and signals in the dotted-line boxes represent the switch module’s internal signal.
Figure 13:.Available trigger sources for watchdog timer overflow
The watchdog timer overflow interval can be programmed through Windows API. After enabling the watchdog timer, users must periodically reset the timer by software command. If the timer is not being reset within the specified interval, the switch module will generate an overflow signal and set the relay pattern to the one specified by users.
This function is disabled by default. For more information, please refer to the software programming users’ guide.
# Warranty Policy
Thank you for choosing ADLINK. To understand your rights and enjoy all the after-sales services we offer, please read the following carefully:
1. Before using ADLINK’s products please read the user manual and follow the instructions exactly.
2. When sending in damaged products for repair, please attach an RMA application form.
3. All ADLINK products come with a two-year guarantee, repaired free of charge.
The warranty period starts from the product’s shipment date from ADLINK’s factory.
Peripherals and third-party products not manufactured by ADLINK will be covered by the original manufacturers’ warranty.
End users requiring maintenance services should contact their local dealers. Local warranty conditions will depend on local dealers.
4. This warranty will not cover repair costs due to:
a. Damage caused by not following instructions.
b. Damage caused by carelessness on the users’ part during product transportation.
c. Damage caused by fire, earthquakes, floods, lightening, pollution, other acts of God, and/or incorrect usage of voltage transformers.
d. Damage caused by unsuitable storage environments (i.e. high temperatures, high humidity, or volatile chemicals.
e. Damage caused by leakage of battery fluid.
f. Damage from improper repair by unauthorized technicians.
g. Products with altered and/or damaged serial numbers.
h. Other categories not protected under our guarantees.
5. Customers are responsible for shipping costs to transport damaged products to our company or sales office.
6. To ensure the speed and quality of product repair, please download a RMA application form from our company website: www.adlinktech.com. Damaged products with attached RMA forms receive priority.
For further questions, please contact our FAE staff.
ADLINK: service@adlinktech.com
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