US Logic Omni III
                           Cache Memory               Faxback Doc. # 17549

The motherboard provides options for configuring the external cache RAM to
either 128KB, 256KB, 512KB or 1 MB.

Cache Memory Configurations:

Each secondary cache memory configuration requires one 15ns tag SRAM and 
four 15 ns data SRAMs. 

Cache Configuration
┌─────────────────┬──────────┬──────────────────────┐
│Cache Size       │Tag       │        SRAM          │
│                 │U27       │ Bank 0  ││ Bank 1    │
│                 │          │ U19-U22 ││ U29-32    │
├─────────────────┼──────────┼─────────┼┼───────────┤
│128KB            │32KB x 8  │32KB x 8 ││           │
│256KB            │32KB x 8  │32KB x 8 ││ 32KB x 8  │
│256KB            │64KB x 8  │64KB x 8 ││           ┤
│512KB            │64KB x 8  │64KB x 8 ││64KB x 8   │
│512KB            │128KB x 8 │128KB x 8││           │
│1 MB             │128KB x 8 │128KB x 8││128KB x 8  │
└─────────────────┴──────────┴─────────┴┴───────────┘
NOTE:  Use chips of the same speed (15ns) throughout the system to
       avoid memory problems.

┌─────────────────────────┐
│Main Logic Board Layout: │
└─────────────────────────┘
                                                
     ┌────────────────────────────────────────────────────────────────────┐
     │        ........DRAM............          ........SRAM..........    │
     │        . ┌───────────────────┐.        B .┌┬───────┐ ┌┬──────┐  B  │
     │        . ├────────────────SI1┤.        A .└┴─U19───┘ └┘U29─q─┘. A  │
     │        . ├────────────────SI2┤.        N .┌┬───────┐ ┌────── ┐. N  │
     │        . ├────────────────SI3┤.        K .└┴─U20───┘ └─U30── ┘  K  │
     │        . └────────────────SI4┘.        1 .┌┬───────┐ ┌────── ┐  0  │
     │        ........................        .  └┴─U21───┘ └─U31── ┘  .  │
     │                                        .  ┌┬───────┐ ┌────── ┐  .  │
     │                                        .  └┴─U22───┘ └─U32── ┘  .  │
     │                                        ..........................  │
     │                                                                    │
     │                                                                    │
     │      ┌──────────────┐                                              │
     │      └───PCI3───────┘                                              │
  B  │                                     ┌────────────────┐             │
  a  │      ┌──────────────┐               │                │             │
  c  │      └───PCI2───────┘               │                │             │
  k  │                                     │                │             │
     │      ┌──────────────┐               │                │             │
     │      └───PCI1───────┘               │                │             │
  o  │                                     │                │             │
  f  │┌────────────┬────────┐              │                │             │
     │└SL1─────────┴─SL5────┘              └────────────────┘             │
  p  │                                     Tag RAM                        │
  u  │┌────────────┌────────┐             ┌┬──────────┐                   │
  t  │└SL2─────────┴─SL6────┘             └┴───U27────┘                   │
  e  │                                                                    │
  r  │┌────────────┬────────┐ ┌────────┐                                  │
     │└SL3─────────┴─SL7────┘ └─VE1────┘                                  │
     │                                                                    │
     │┌────────────┬────────┐ ┌────────┐                                  │
     │└SL4─────────┴─SL8────┘ └─VE2────┘                                  │
     └────────────────────────────────────────────────────────────────────┘

Secondary Cache Memory
┌────────┬─────┬──────┬──────┬──────┬──────┬───────┐
│Jumper  │128KB│ 256KB│ 256KB│ 512KB│ 512KB│ 1MB   │
│        │     │ 32x8 │  64x8│ 64x8 │ 128x4│ 128x8 │
├────────┼─────┼──────┼──────┼──────┼──────┼───────┤
│JP13    │Open │Close │Close │Close │Close │Close  │
│JP14    │Open │Open  │Open  │Close │Close │Close  │
│JP16    │Open │Open  │Open  │Open  │Open  │Close  │
│JP25    │Open │Open  │Open  │Open  │1-2   │2-3    │
│JP27    │2-3  │1-2   │2-3   │1-2   │2-3   │1-2    │
│JP29    │Open │Open  │1-2   │2-3   │1-2   │2-3    │
└────────┴─────┴──────┴──────┴──────┴──────┴───────┘

┌──────────────────┐
│Installing SRAMs: │
└──────────────────┘

Note: Static electricity can destroy electronic devices.  Whenever
      you handle any option outside of its protective packaging,
      first discharge any static electricity from your body by
      touching a protective grounding device or unpainted metal on
      the rear panel of the system unit.

To install SRAMs:

1. Turn off the computer, and disconnect all cables.
2. Discharge any accumulated static electricity from your body by
   touching a grounded metal object. Then, open the computer.
3. Remove any expansion adapters installed in the three-slot expansion
   area by removing the expansion slot screws, disconnecting any data
   cables, and gently moving each adapter back and forth while pulling
   it out of the riser card connector.
4. Locate the appropriate SRAM sockets
5. The two rows of pins are probably splayed too far apart and must
   be angled closer together before installation.

   Rest the side of the chip on a hard and even surface.
   Carefully and steadily push down the chip until the pins are
   at a right angle with the chip body.  Repeat for the other side.

6. Align the notch end in each SRAM with the notch on the socket. Being
   careful not to bend the pins, insert the chip's pins into the
   corresponding holes in the socket.  Press down on the SRAM until it is
   fully inserted.
7. Set Jumper block for the new configuration. (See Above Chart)
6. Reinstall any expansion adapters you removed.
7. Be sure the internal cables are securely connected and do not cause
   mechanical interference. Then, close the computer.
8. Reconnect all cables.

(CC/tmc-12/04/95)