Plate\LFI List

I'm still compiling a list of plates for the 8870. If you spot something wrong or missing please let me know.
1530-00
Hardware arithmetic unit HAU (maths co-processor)

The DIP switch settings depend on the NIROS release running.
The difference in DIP coding is caused by the fact that pre-NIROS 7.0 a system could only have one CPU, thus only one HAU. From 7.0 onwards up to 4 CPUs were supported, so consequently up to four HAUs could be added also.
1537-01 

    


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1641-00
CPU module (2 plates) + internal memory 512K (1 plate)

The connector on the middle plate goes to the CPU status display that's mounted on the chassis. The other connector was used for connecting the engineering system diagnostic tool.
Because the machine can only support one of these CPUs, there are no DIP switches required.

The memory is internal so it's starting address will always be $0000 meaning again, no configuration switched are required.
Notice from the images that it appears the memory board started out as a 256K version, but was later updated (probably during a repair) to it's maximum 512K
1642-00
512Kb External Memory
1642-01
256Kb External Memory
1860-02
PLC 2 Channel (Programmable Line Controller)
1882-00
ALME (Asynchronous Line Multiplexer Extended)
When the plate is installed in the chassis, the lower 15 way connector is always channel #0, and channel #0 on the first ALME is always connected to the master port. It will usually have a V24+remote switch on card fitted within the ALME, but not always. The middle picture on the right shows a standard V24 card installed without the remote switch on relay.

The 00 version of this plate used personality interface boards with little fragile gold pins that had to be perfectly aligned to the main board. Quite often, if you were rushing or the light was bad you would insert a board and one of the pins would bend or even snap.

​Channel #1 seems to be reserved by the operating system for connection to a modem. Don't try and connect a VDU to this channel.

There is additional technical info here.
1882-01
ALME (Asynchronous Line Multiplexer)
Specification wise, the 1882-01 is almost identical to the 1880-00 board. The only real difference is that it uses different personality interface boards. These boards no longer have fragile pins, but standard 0.1" spaced DIN sockets, and the ALME has sturdy pins.

There is additional technical info here.
1883-01/02
5 1/4" Floppy Disc Controller
On one of the M25s I've got, there is an 1883-01 controller installed connected to an 8" FD but according to the information I have, this configuration isn't valid. This could explain why the system behaves erratic when this plate is installed and configured. I always thought it may have been faulty, but perhaps being connected to an 8" FD is what's causing the problem.
2549-00
MD/SMC Controller 
With the plate installed in the chassis, the top connector goes to the SMC drive, and the bottom goes to the cable connected to the backplane that connects to the disc drive.
3038-02
Battery Backup
PLEASE SERVICE THIS PLATE AS SOON AS POSSIBLE !!!

This plate was designed to keep the CPU, memory and possibly other boards that contains state information alive in the event of a power failure. A fully charged battery pack in good condition would good for around 20 minutes if I remember correctly, but it of course depended on the load.

It also contained the CPU reset switch - I never understood why it wasn't on the CPU.

This plate should contain a NiCad battery pack, but as is common to find now, the pack had leaked. You can see the stains left on the aluminium bottom cover. If this had been left a bit longer, the acid from the batteries would have eaten the cover, and the rest of the plate as well.

I seem to remember that you could add "slave" plates to increase the capacity and small black jumper cables were connected to the two sockets on the top.

You don't need to have the battery pack, and in fact, you would do better connecting the entire machine to a modern UPS these days. It would give you time to shutdown cleanly and is probably cheaper than then cost of replacing the NiCad's. However, you MUST have this plate installed else the PSU won't start and the will behave very oddly.

I also remember seeing a system with two of these plates installed; it was a mistake I think but the system still ran fine.

Some information here on servicing this plate here.
3109-02
Chassis PSU
The PSU has it's own dedicated slot on the backplane, always on the far left. Typically each backplane or tier would have it's own PSU but this certainly isn't the case for the M25 and the one PSU runs everything including the fans.

There are a couple of fuses inside that are worth checking over if a PSU fails, however, this is the one unit that has high capacitance capacitors installed and these are going to be troublesome because of their age.

DO NOT go poking around with your fingers inside this module if you don't know what you're doing, even when it's removed from the chassis. There's a high voltage capacitor that could hold a lethal charge. Remove the PSU, let it stand for 5 or 10 minutes before you open it up, and be carful where and what you touch.

When I get a chance I will be adding a supplementary page on these PSUs.
3630-05
M25 Peripheral Tier (top level) backplane
This is the peripheral backplane and can accommodate three devices made from a combination of fixed disks, SMC and Floppy Disk drives but exactly what combination and how many depends.

The left-hand slot seems dedicated to the SMC drive. You will see that it doesn't have a black mains power connector. If you look at image of the backplane reverse, you will see there are three IDC connectors. The one located on the right-hand edge at the top connects directly too this SMC slot, however, this connector isn't actually used.

The middle slot is for the fixed disk drive and it's data connectors are terminated at the FP (Fixed Platter) Contr. connector on the rear of the backplane. Cable 7428-00 connects from here to the system controller.

The remaining slot is multi-purpose. On most systems it seems to be configured for either a floppy disk drive, or not used.

If there is a floppy disk installed, a cable connects from the FD-Controller connector to the floppy disk controller.

However, this 3rd slot "can" accommodate a second fixed disk drive. If you look at the picture showing the gold front of the backplane, there is a cut-out at the top located between the middle and right slot connectors. If you can see just gold pins, then the right-hand slot is isolated from the disk controller bus, and can be used for a floppy disk drive; as long as a suitable cable is connected to the connector on the rear.

However, if there is a bridging connector in-place, then the right-hand slot is connected to the disk controller bus and can be used to support a second disk drive.