IES20000431A2 - A switching system - Google Patents

Abstract

A switching system (1) connects with a host computer (6) via a GPIB bus (5). A controller (3) in a chassis (2) slot transmits control signals to up to twelve switch modules (4). A passive backplane (20) is used to address the modules (4) according to voltage levels sensed on pins (A15-A18) in the connectors. The controller (3) uses the backplane to provide a 16-bit data bus (21), a module address bus (22), a register address bus (23), a control bus (24), an auxiliary bus (24) and a power supply bus (25).

Description

“A switching system” The invention relates to a switching system for signal routing between instruments in testing and/or data acquisition environments, and comprising a chassis housing a power supply unit, a control module, and switch modules inserted in racks of the chassis.

Such a system is described in PCT Patent Specification No. 90/08327 (ThomsonCSF). This system interfaces between a hyperfrequency integrated circuit and the probes of an analyser and is arranged in a modular manner.

While this system is apparently quite effective for the above application, there is still a need for a switching system which allows dynamic reconfiguration of resources and a large frequency range, from DC and high voltage LF to 1000 MHz RF and Lightwave. These requirements are particularly important for many automated test and data acquisition applications According to the invention there is provided a switching system comprising a chassis, a controller, and a plurality of switch modules inserted in racks of the chassis, characterised in that, the system comprises a passive backplane comprising a push-fit connector for connection of each switch module to the controller, means in the controller for using passive lines of the backplane as an address bus for addressing switch modules, and for using passive lines of the backplane as a control bus for transmitting control signals to switch modules, and for using passive lines of the backplane as a data bus for communication of data with switch modules, and the controller comprises a computer interface for interfacing of the system with a host system. -2IE000431 In one embodiment, the backplane comprises means for individually applying in a permanent manner a voltage to each pin of a set of pins in each switch module connector, each switch module comprises means for detecting said voltage levels and converting them to a unique address associated with the slot in which the switch module is currently inserted, and the controller comprises means for addressing switch modules on the address bus using said addresses.

In one embodiment, a voltage is applied to each of a set of four pins in each switch module connector.

In one embodiment, the voltage is either floating or ground, and each switch module comprises means for associating one bit level to floating and another bit level to ground.

In another embodiment, each switch module comprises means for informing the control module of its switch resources, correlated to the current address.

In one embodiment, the controller comprises means for placing a module identification flag on the control bus together with a switch module address on the address bus to poll return of status data identifying the switch module and its revision.

In one embodiment, each switch module comprises means for asserting a controller interrupt request on the control bus.

In one embodiment, the controller comprises means for using passive lines of the backplane as a register address but for asserting read or write access to unique registers on switch modules.

IE000431 -3In one embodiment, the controller comprises means for transmitting general asynchronous reset commands for all switch modules and for transmitting asynchronous module-specific reset commands in conjunction with the module address on the control bus.

In one embodiment, the backplane is connected to a power supply, and power of different voltage levels is provided on lines of the backplane.

The invention will be more clearly understood from the following description of some embodiments thereof, given by way of example only with reference to the accompanying drawings in which :Fig. 1 is a perspective view of a switching system of the invention; Fig. 2 is a diagrammatic representation of a backplane of the switching system; and Fig. 3 is a diagrammatic representation of the software architecture of a system controller of the system.

Referring to Fig. 1, the system comprises a chassis 2 having racks supporting a system controller 3 and up to twelve switch modules 4. The system controller 3 and die switch modules 4 are interconnected at the back of the chassis 2 by a backplane, described in more detail below. The system 1 is shown connected to a host system 6 by a General Purpose Interface Bus (“GPIB”) at the controller 3. The host interface may alternatively be an RS232 or Ethernet bus, for example.

The controller 3 comprises embedded circuits to perform the following main functions: -4IE000431 host computer interfacing, MMI (man-machine interface) comprising an LCD display 7, a keypad 8 and associated functionality, a backplane driver, and application software including a parser, system housekeeping, error handler, and switch module interrupt handler.

The switch modules 4 comprise general purpose RF or optical switches and the system 1 may include switch modules 4 which perform complex functions such as signal attenuation, measurement, or digital I/O.

The system 1 is for automated test or data acquisition applications with signal routing between instruments. The controller 3 allows dynamic reconfiguration of signals via a backplane on the basis that each switch module 4 automatically “knows” its address by sensing its location in the chassis 2. The controller 3 routes signals according to this address, as described in more detail below. The backplane uses an asynchronous 8/16 bit bus transfer protocol.

The controller 3 picks up simple command strings from the host system 6 via the GPIB bus 5, interprets them, and opens or closes switches on the switch modules 4. A 40 MHz clock provides clock signals to both a GPIB chip and the microprocessor, and a 48 MHz clock is provided for a USB chip. An FPGA has the following functions.

Generate Chip Selects for the registers and buffers, backplane buffer, front panel, I1 2C Out, parallel port out, LED out, and Switch in.

Generate BE8 signal (8 bit access) when PROM, RAM,FLASH are selected -5IE000431 EEPROM Interface.

Interrupt routing from front panel (if required).

Single bit output to watchdog The controller also includes an EEPROM storing configuration data for FLASH memory, and data in an EPROM is used in default if the EEPROM is empty.

Communications with the switch modules 4 is via the backplane 20, shown in schematic format in Fig. 2. The backplane 20 comprises a connector for each switch module 4 and one for the controller. The controller 3 and the switch modules 4 are simply push-fitted into the connectors as guided by the chassis 2. The backplane 20 is made from double sided FR4, 1.6mm PCB, flammability rated at VO. The outline dimensions are 426.9mm x 129.7mm. The backplane board is finished in green solder mask and has Hot Air Leveled finish on all pads and PTH. There is white silkscreen on the front of the board. The connectors are of type DIN41612 Connector Socket Form A-C, 96 way, with oils rows A and C (A1-A32, C1-C32) used. Two Load 120 Ohm 6W resistors are used on the plus and minus 12Volt power supply lines to ensure that the minimum load is applied to the power supply. 11 x 220 Ohm 4W Wire wound resistors are used on the +5 Volt line to ensure that the minimum power supply load is maintained. The power supply is mounted in the chassis 2. All load resistors are raised from the board using ceramic beads to prevent heat damage to the PCB surface. 11 x luF Capacitors are used for de-coupling. One six pin vertical pin connector is used to allow connection to the plus and minus 12Volt supply is via a push on socket. Two screw terminals are included for the +5 Volt supply connection.

The backplane circuit hoard is laid out in a way such that all of the connectors are facing forward. All other components are mounted on the rear of the backplane board. When mounted in the chassis 2, provision is made for the controller 3 to be IE000431 -6inserted in the left-most position. All switch modules 4 are mounted to the right of the controller slot, beginning with slot 1 and ending with slot 12.

At the connectors, four of the pins (A15-A18) are not used by the controller 3 for 5 signalling. Instead, on the backplane 20 they are connected to the ground or are floating (not connected, N/C) on an individual basis at each connector. The combination of GND and N/C for the four pins A15-A18 in each connector provides a 4-bit slot address S0-S3. When a switch module 4 is inserted into a slot in die chassis, it automatically reads the signals on these four pins to determine the address. The SO to S3 addresses are as set out in Table 1 below.

Slot Number SO SI S2 S3 1 N/C GND GND GND 2 GND N/C GND GND 3 N/C N/C GND GND 4 GND GND N/C GND 5 N/C GND N/C GND 6 GND N/C N/C GND 7 N/C N/C N/C GND 8 GND GND GND N/C 9 N/C GND GND N/C 10 GND N/C GND N/C 11 N/C N/C GND N/C 12 GND GND N/C N/C Table 1 The S0-S3 address is hard-coded, being set by physical connections for the pins A1515 A18 on an individual basis in each connector. Indeed, the full backplane 20 is passive, and it delivers control signals only when such signals are put onto the IE000431 -7remaining pins A1-A14, A19-A32, and C1-C32. The following Table 2 set out the configuration.

Slot Cont. Switch Slot Controller Switch Reference DIN41612 (Slot-O) Modules (Slots 1-12) Reference DIN41612 (Slot-0) Module (Slots 1-12) Al GND 0 Volts Cl GND 0 Volts A2 VCC +5 Volts C2 VCC + 5 Volts A3 Chassis GND Chassis GND C3 Future 1 Future 1 A4 Chassis GND Chassis GND C4 Future 2 Future 2 A5 +12 Volts + 12 Volts C5 +12 Volts +12 Volts A6 + 12 Volts + 12 Volts C6 + 12 Volts + 12 Volts A7 Future 4 Future 4 C7 R8 R9 A8 Future 5 Future 5 C8 R9 RIO A9 -12 Volts -12 Volts C9 RIO Rll A10 -12 Volts -12 Volts CIO /CARD ID /CARD ID All I2C I2C Cll R/W R/W A12 I2C I2C C12 CLEAR CLEAR A13 IACK IACK C13 RESET RESET A14 IRQ IRQ C14 /STROBE /STROBE A15 N/C S3 C15 CS3 CS3 A16 N/C S2 C16 CS2 CS2 A17 N/C SI C17 CS1 CS1 A18 N/C SO C18 CSO CSO A19 R7 R7 C19 R3 R3 A20 R6 R6 C20 R2 R2 A21 R5 R5 C21 Rl Rl A22 R4 R4 C22 RO RO A23 D15 D15 C23 D7 D7 -8IE000431 A24 D14 D14 C24 D6 D6 A25 D13 D13 C25 D5 D5 A26 D12 D12 C26 D4 D4 A27 Dll Dll C27 D3 D3 A28 DIO DIO C28 D2 D2 A29 D9 D9 C29 DI DI A30 D8 D8 C30 DO DO A31 VCC +5 Volts C31 VCC +5 Volts A32 GND 0 Volts C32 GND 0 Volts Tai >le2 Referring again to Fig. 2, the backplane 20 comprises the following buses. 21: A 16-bit bi-directional data bus terminating in pins A23-A30 and C23-C30. 22: Card address bus for transmitting CSO -CS3 as detected by the switch modules 4, described above. This terminates in pins C15-C18. The switch modules 4 derive a card enable signal from this bus. 23: Register address bus to access unique read or write registers on the addressed card, terminating in pins A19-A22, C7-C9, and C19-C22. The address bus provides up to 2048 addresses per system card (2K words/4K bytes). Paged or I/O decoding is provided on each card as necessary. 24: A control bus for: Asynchronous reset control, decoded by all switch modules 4. This terminates with pin C13.

IE000431 -9Asynchronous slot-specific reset commands in conjunction with the card address bus 22 to reset a particular module 4. This terminates in pin C13 and the address pins C15-C18.

Data strobe. Data written by the controller is valid on the falling edge and data is read by the controller on the falling edge during a read cycle.

A read/write line terminating at pin All. This is asserted by the controller 3 to signify a read or write cycle. Read cycles are signified by a logic high, and write cycles by a logic low.

IRQ, namely an interrupt line terminating at pin A14. This is monitored by the controller 3 and asserted by one or more modules 4 requiring service. IRQ is unasserted by the interrupting module during an interrupt acknowledge sequence. IRQ is connected in a wire-Or configuration to all slots.

IACK (Interrupt Acknowledge), using pin A13, asserted by the controller to indicate an IRQ acknowledge sequence. When IACK is active, the addressed module 4 returns to an IRQ status bit.

An auxiliary control signal for module identification, appearing at pin CIO and using the module address bus. When this line is active the currently addressed module returns a status byte on the data bus. The status bus identifies the module type and revision. Module ID may also be used in conjunction with the module register address lines to access an additional non-volatile memory area containing manufacturing and calibration information.

IE000431 -1024: Auxiliary bus of lines reserved for future use, at pins A7, A8, Al 1, and A12.

: A power supply bus providing 5V, 12V, and -12V at pins A5, A6, A9, A10, A31, C5, C6, and C31.

Referring now to Fig. 3, the control architecture of the controller 3 is illustrated. The various system level commands 30, module level commands 31, and module specific commands 32 are as described above. A computer interface 33 is used for software queries of input/output messages from input/output interface handlers including one or more interfaces including GPIB, MMI, serial, USB, and Ethernet. A command parser 34 receives all commands 30, 31, and 32 and decodes and executes them. Examples of system level commands are *RST for resetting the system and IDN? for return of system ID string. Examples of module-common commands are CLR to reset a module and ID? to return a module ID. Examples of module-specific commands are CL to close a module relay and WR to write a digital value to a module.

The bus communication driver 35 comprises layered proprietary calls which perform the following basic bus I/O activities. Data is passed to and from the main message queue based parser executive: Layer 1 - Card Write, Card Read, Backplane Reset, Card Reset.

Layer 2 - Card Identify, Interrupt Service/Acknowledge The final block is the module-level hardware and firmware 36 comprising decode logic, data buffering, local power up reset, and optionally, execution engine and memory.

It will be appreciated from the above that the system 1 allows excellent versatility. Switch modules may be connected in any slot because they automatically recognise IE000431 -11their address. The control module thus simply places the address on the bus and only the relevant switch module will recognise the address and read the control commands. The switch module configuration is automatically maintained in the controller 3 by each switch module 4 using the bus to inform the controller 3 of its resources correlated to the CS0-CS3 address.

The invention is not limited to the embodiments described, but may be varied in construction and detail within the scope of the claims.

Claims (5)

Claims

1. A switching system comprising a chassis (2), a controller (3), and a plurality of switch modules (4) inserted in racks of the chassis (2), characterised in that, the system comprises a passive backplane (20) comprising a push-fit connector for connection of each switch module (4) to the controller, means in the controller for using passive lines of the backplane as an address bus (32) for addressing switch modules (4), for using passive lines of the backplane as a control bus (24) for transmitting control signals to switch modules, and for using passive lines of the backplane as a data bus (21) for communication of data with switch modules (4), and the controller comprises a computer interface (5) for interfacing of the system with a host system (6).

2. A switching system as claimed in claim 1, wherein the backplane (20) comprises means for individually applying in a permanent manner a voltage to each pin of a set of pins in each switch module connector, each switch module (4) comprises means for detecting said voltage levels and converting them to a unique address associated with the slot in which the switch module (4) is currently inserted, and the controller (3) comprises means for addressing switch modules (4) on the address bus using said addresses.

3. A switching system as claimed in claim 2, wherein a voltage is applied to each of a set of four pins in each switch module connector, and wherein the voltage is either floating or ground, and each switch module comprises means for associating one bit level to floating and another bit level to ground. IE000431 -134. A switching system as claimed in claims 2 or 3, wherein each switch module comprises means for informing the control module of its switch resources, correlated to the current address, and wherein the controller comprises means for placing a module identification flag on the control bus together with a

4. 5 switch module address on the address bus to poll return of status data identifying the switch module and its revision.

5. A switching system substantially as described with reference to the drawings.