PXML No. 47
APPROVAL No. NS/3343/123/G/452428 and NS/3343/123/G/452429 DDI

Cabinet layout (ISDX-S)
The majority of the equipment defining the ISDX-S is in the form of printed wiring cards, accommodated by two card cages in the ISDX-S and a single card cage in the ISDX-MN which occupy the top sections of the robust, single bay, sheet steel cabinet. Where the requirement is for a standard system of up to 96 extensions and 16 trunks, only the bottom card cage is equipped. Removable front and rear preformed panels, fitted with individual locks for maximum security, allow access to the card cages. The cabinet is mounted on four castors, two movable and two locked, for ease of movement.

Forced air ventilation is provided by five fan units mounted in a tray assembly, located under the bottom cage. Two thermal switches monitor the temperature inside the cabinet such that should the temperature exceed 60 degrees an urgent alarm is raised and if 70 degrees is exceeded, the cabinet power is automatically switched off. Air is drawn in through a foam covered, steel mesh filter which is mounted horizontally across the cabinet floor aperture. The filter is easily extracted for cleaning by removing the filter cover at the bottom front of the cabinet, after releasing the two turn spring fasteners.

In the ISDX-S, the power supply modules and double floppy disk drive (DFDD) autoloader unit are mounted on a steel chassis in the lower portion of the cabinet to give optimum stability. Access is again by removable locking panels. Note that on refitting a panel, the lock is located near the uppermost edge on all panels except the lower rear panel, identified by the cut-out for the mains Input cable (AC version only), which must be refitted with the lock at the bottom. The mains AC input to the AC powered cabinet, is supplied via a fused spur, and is switched by the circuit breaker located at the rear of the cabinet on the lower R.H. side. The DC powered version is supplied from the power cabinet Mk 11 to bolted connections on terminal block TB17.

Note: Earth straps are fitted at the cabinet doors.

Printer access is via the V.24 interface connector mounted horizontally on the lower front panel, in the vicinity of the autoloader.

Four variants of the cabinet are available which provide a choice of AC or DC, 2A or BA PSU systems. The advantage of the 8A PSU system is that the shelf capacity may be increased since more power is available. The choice of AC or DC power will depend on the site. The power for the AC version is taken from the 24Ov mains supply. The DC version is powered from -50v supplied by a power cabinet. The part number for each variant is as follows:
87111/13110/003   AC, 2A PSU
87111/13110/004   DC, 2A PSU
87111/13110/005   AC, 8A PSU
87111/13110/006   DC, 8A PSU

Where only the lower cage, of a two card cage system, is equipped, line PSU L2, the intershelf bus, the shelf LIF backplane and all associated cabling, are omitted.

Cabinet layout (ISDX-MN)
In the ISDX-MN cabinet a single card cage is fitted in the bottom of the cabinet. Forced air ventilation is provided by three fan units fitted between the card cage and the power supply and autoloader units fitted above the card cage. The mains supply is fed to the cubicle via a mains on/off switch and a fuse at the rear of the cabinet. The DFDD autoloader is fitted at the top of the cabinet. The cabinet part number for the ISDX-MN is 87111/13127/000.

Card cages
Two card cages are mounted in the cabinet of the ISDX-S one above the other to form shelves occupying the full width of the cabinet. A single card cage is used in the ISDX-MN. The cards comprising the ISDX-S slide into grooved mouldings fixed to the top and bottom of the cage, each cage in the ISDX-S having 33 slot positions available. There are 27 slot positions available in the ISDX-MN.

In the ISDX-S the lower cage and, in the ISDX-MN the only cage, although forming one physical shelf, is divided into two logical shelves, with the first seven slots from the left, viewed from the front of the cabinet, referenced slots A to G, logical shelf 0, and allocated to the computer control group cards. The remaining slot positions numbered 02 to 27 on the ISDX-S and 02 to 21 on the ISDX-MN are denoted logical shelf 1. On the ISDX-S the upper cage is denoted shelf 2 and the slots are numbered 01 to 33 from left to right. Thus, the shelf reference and slot position together, enable any card to be identified by a unique physical address.

System interconnection
Multi-track backplanes mounted across the rear of the card cages connect the cards into the system, the cards plugging into 96-way connectors mounted on the backplanes to correspond to the card cage slot positions. The cards are shaped to allow their P2 rear edge connector to slot into the lower backplane, which occupies the full width of the cage, and their Pl connector to slot into the appropriate upper backplane, when applicable.

Lower backplanes : P2
There are two P2 backplanes, the P2 control backplane is fitted the full width of the bottom card cage and the P2 line backplane, the full width of the top cage on an ISDX-S. The backplanes differ from each other in that the line backplane accommodates only telephony and data groups together with an optional miscellaneous group, whereas the control backplane also accommodates the control group cards and the mandatory miscellaneous group. The parallel tracks of the P2 backplanes, which carry data between each shelf interface card and the relevant telephony or data group, form the inter-shelf bus.

The various voltages provided by the line and ringer PSU to the terminal blocks mounted centrally at the rear of the backplanes, are distributed via the tracking and applied to the cards at the relevant pin (1 to 7).of the backplane slot connector. The DSG and ALM terminal blocks, TB12 and TB16, located on the R.H. rear of the P2 backplanes, are associated with the urgent alarm, initiated by the closing of the thermal switch, should the cabinet overheat.

Upper backplanes
Certain cards operate as individual units to perform a defined function, whereas others inter-act to perform a group function. A group backplane connects the related members of the group, the card upper rear edge connector, Pl, slotting into the corresponding backplane connector. In a number of cases the backplanes are also used to connect preformed cables between the card and the Test Jack Frame (TJF). Dummy backplanes are fitted to the card cage where gaps are left between backplanes, to regulate the airflow within the cabinet.

Inter-shelf bus
In a two cage system (ISDX-S only), the cards occupying the top cage are linked to the control group cards by the inter-shelf bus (ISB) which comprises two entirely separate 64-way ribbon cables, located against the R.H. side panel of the cabinet. 00 The cables differ in the wiring of the terminating connectors such that one cable, coded 000 or X, is associated with the data present at the A and C pins of an upper, Pl, backplane slot connector and the other cable, coded 001 or Y, is associated with the data present at the A and B pins. Both sets of data are carried in an alternate earth/signal format to avoid cross talk.

Preformed cables
Preformed cables provide the transmission path between interface cards of the telephony and data groups and the TJF for connection to the external network. The cables are connected into the rear of the relevant upper backplane slot connectors.

Control group
The control group cards are located in the bottom card cage, occupying slot positions A to G, denoted logical shelf 0. The cards forming the group are:

Slot A   Empty slot
Slot B1   Megaword Memory and Controller
Slot C   CPU 1
Slot D   CPU 2
Slot G   Digital Switch Controller

The Shelf interface card located in slot 2, logical shelf 1 may also be considered as a member of the control group as it connects into the Pl control group backplane. A second Shelf interface card is located on shelf 2, slot 2, when a two card cage system is installed, being linked into the system via the inter-shelf bus.

Each card must occupy the correct slot position.

The Serial 110 interface and the Delta channel controller, physically occupy slots E and F respectively but are not direct functional members of the control group. The Delta channel controller card must be fitted for networking.



P2	06496/00X	Control	33	All cards in the bottom cage

	06540/001	Control	27	All cards

	06498/000	Line	33	All cards in the top cage

PI	06494/00X	Control	7	1 Megaword memory and
	06538/000			memory controller
					CPU 1; CPU 2; Serial I/O;
					Delta channel controller;
					Digital switch controller; Shelf I/F

	06420/000	Shelf I/F 2	Top cage Shelf I/F. If supplied the
					Rotary register occupies slot 1 but
					does not connect into the Pl B/P

	06416/00X	Miscellaneous	3	General purpose I/O; Bypass;
					Modem; Console I/F

	06410/00X	Trunk	6	Codec; Trunk controller;
					4 x Trunk interfaces

	06412/00X	Extension 6	3 x Codec; 3 x Extension I/Fs
				or	or
	06414/00X		2	Codec; Extension I/F

	06572/000	ISDT	1	ISDT interface, Modem, Terminal
					server or ALI

	06592/000	DLI	1	Digital link interface

Note:- indicates fitted to an ISDX-S only and # indicates fitted to an ISDX-MN only.

Miscellaneous groups
The miscellaneous group comprises a combination of the cards listed below, the exact combination being configured to suit the site requirements. The slot position referenced is that which the card would occupy on an ISDX-S 9 all the members of the group were required on a one card cage system. On an ISDX-MN the second bypass card Is not fitted, and the slot is referred in brackets below.

Common equipment card   Slot 22
Bypass   Slot 23
Console interface   Slot 24 (18)
General purpose   Slot 25 (19)
Bypass   Slot 26 (20)
Modem   Slot 27 (21)

The upper rear edge connectors, Pl of the card occupying slots 25, 26 and 27 (or 18, 19 and 20) plug into the 3-slot miscellaneous backplane. The remaining cards may be directly linked into the system with the necessary cabling connecting to the Pl connector on the card.

If a two card cage system is used the miscellaneous group cards can occupy any of slots 25 to 27 of shelf 01 and slots 31 to 33 of shelf 02. Normally the General purpose I/O card, Bypass card and Modem card occupy slots 25 to 27 of shelf 01 and the Console interface card and Common equipment card occupy slots 32 and 33 of shelf 02. The Modem cards being wider must always occupy the slot at the extreme right (slot 27 or 33).

In the ISDX-MN the miscellaneous group is fitted in slots 18, 19 and 20 with the Modem card fitted separately from the miscellaneous group in slot 21 by using an ISDT backplane for interconnection.

Telephony groups
The remaining slot positions on the bottom card cage are normally occupied by trunk and extension groups in the standard configuration of 96 extensions and 16 trunks. The top cage is used to accommodate trunk, extension and data groups, the quantities, mix and slot positions being entirely dependent on the precise site requirements. The remaining slot positions in the card cage on an ISDX-MN are used for trunk, extension and data groups.

Trunk groups
A trunk group is capable of handling sixteen channels, comprising six cards connected into the system via the associated six slot trunk backplane. The group must contain a codec and a trunk controller, the remaining four cards being various combinations of exchange and IPBX interfaces as determined by the customer's requirements.

Extension groups
An extension group comprises a codec and an extension Interface, each group capable of handling sixteen channels, which may be all short line, all long line or the specific twelve short and four long line mix. Two backplanes are available to connect the cards into the system, one a two slot backplane accommodating one group and the other a six slot backplane accommodating three groups.

Double floppy disk drive (DFDD) autoloader
The DFDD autoloader is mounted on the cabinet lower front panel of an ISDX-S and is a TEAC F35 GF double floppy disk drive fitted with system controller and disk controller cards. The same autoloader unit is fitted at the top of an ISDX-MN.

The unit is normally loaded with the current system software disk and a back-up disk, supplied separately. During system operation the contents of the current system software disk are loaded into the memory of the ISDX-S and used to control the system. By use of a DUMP command the contents of the ISDX-S system memory can be copied onto the backup disk. This up-to-date dumped data can then be used should a system reload become necessary.

Floppy disks
The disks used by the ISDX-S are 3.5 inch MDF-2HD high density micro floppy disks. They are supplied in plastic cases with spring loaded covers over the disk surface. The disks must be handled with care to avoid corruption of the stored data. The precautions listed below must be strictly observed:-

1. Check that the correct type of disk is being used.
2. Do not touch the shiny surface of the disk exposed in the jacket windows.
3. Do not bend the disk.
4. Replace the disk in the storage folder or file when not in use.

ISDX Brochure

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Last revised: December 22, 2021